LVIV, Ukraine (AP) — Russian forces intensified shelling of cities in Ukraine’s center, north and south, a Ukrainian official said, upending attempts to evacuate besieged civilians. With the Ukrainian leader urging his people to fight in the streets, Russian President Vladimir Putin shifted blame for the invasion, saying Moscow’s attacks could be halted “only if Kyiv ceases hostilities.”

The outskirts of Kyiv, Chernihiv in the north, Mykolaiv in the south, and Kharkiv, the country’s second-largest city, faced stepped-up shelling late Sunday, presidential adviser Oleksiy Arestovich said. Heavy artillery hit residential areas in Kharkiv and shelling damaged a television tower, according to local officials.

“This is likely to represent an effort to break Ukrainian morale,” the U.K. Ministry of Defense said of Russian tactics as the war entered its 12th day Monday. Fighting has caused 1.5 million people to flee the country, which the head of the U.N. refugee agency called “the fastest-growing refugee crisis in Europe since World War II.”

The most recent attacks dashed hopes that more people could escape the fighting in Ukraine, where Russia’s plan to quickly overrun the country has been stymied by fierce resistance. Russia has made significant advances in southern Ukraine and along the coast, but many of its efforts have become stalled, including an immense military convoy that has been almost motionless for days north of Kyiv.

Food, water, medicine and almost all other supplies were in desperately short supply in the southern port city of Mariupol, where Russian and Ukrainian forces had agreed to an 11-hour cease-fire that would allow civilians and the wounded to be evacuated. But Russian attacks quickly closed the humanitarian corridor, Ukrainian officials said.

“There can be no ‘green corridors’ because only the sick brain of the Russians decides when to start shooting and at whom,“ Interior Ministry adviser Anton Gerashchenko said on Telegram.

A third round of talks between Russian and Ukrainian leaders is planned for Monday.

Ukrainian President Volodymyr Zelenskyy rallied his people to remain defiant, especially those in cities occupied by Russians.

“You should take to the streets! You should fight!” he said Saturday on Ukrainian television. “It is necessary to go out and drive this evil out of our cities, from our land.”

Zelenskyy also asked the United States and NATO countries to send more warplanes to Ukraine. But that idea is complicated by questions about how to provide aircraft to Ukrainian pilots.

He later urged the West to tighten its sanctions on Russia, saying that “the audacity of the aggressor is a clear signal” that existing sanctions are not enough.

A senior US defense official said Sunday that the U.S. assesses that about 95% of the Russian forces that had been arrayed around Ukraine are now inside the country. The official said Russian forces continue to advance in an attempt to isolate Kyiv, Kharkhiv and Chernihiv, but are being met with strong Ukrainian resistance.

The official, who spoke on condition of anonymity to discuss military assessments, said the convoy outside Kyiv continues to be stalled.

As he has often done, Putin blamed Ukraine for the war, telling Turkish President Recep Tayyip Erdogan on Sunday that Kyiv needed to stop all hostilities and fulfill “the well-known demands of Russia.”

Putin launched his invasion with a string of false accusations against Kyiv, including that it is led by neo-Nazis intent on undermining Russia with the development of nuclear weapons.

The Russian Defense Ministry on Sunday announced that its forces intend to strike Ukraine’s military-industrial complex with what it said were precision weapons. A ministry spokesman, Igor Konashenkov, claimed in a statement carried by the state news agency Tass that Ukrainian personnel were being forced to repair damaged military equipment so that it could be sent back into action.

Zelenskyy criticized Western leaders for not responding to Russia’s latest threat.

“I didn’t hear even a single world leader react to this,” Zelenskyy said Sunday evening.

The Russian Defense Ministry also alleged, without providing evidence, that Ukrainian forces are plotting to blow up an experimental nuclear reactor in Kharkiv and to blame it on a Russian missile strike.

Putin and French President Emmanuel Macron spoke Sunday about the nuclear situation in Ukraine, which has 15 nuclear reactors at four power plants and was the scene of the 1986 Chernobyl nuclear disaster.

The men agreed in principle to a “dialogue” involving Russia, Ukraine and the U.N.’s atomic watchdog, according to a French official who spoke on condition of anonymity, in line with the presidency’s practices. Potential talks on the issue are to be organized in the coming days, he said.

Putin also blamed the fire last week at the Zaporizhzhia nuclear plant, which Ukrainian officials said was caused by Russian attackers, on a “provocation organized by Ukrainian radicals.”

International leaders, as well as Pope Francis, appealed to Putin to negotiate.

In a highly unusual move, the pope said he had dispatched two cardinals to Ukraine to try to end the conflict.

“In Ukraine, rivers of blood and tears are flowing,” the pontiff said in his traditional Sunday blessing.

The death toll remains unclear. The U.N. says it has confirmed just a few hundred civilian deaths but also warned that the number is a vast undercount.

About eight civilians were killed by Russian shelling in the town of Irpin, on the northwest outskirts of Kyiv, according to Mayor Oleksander Markyshin. The dead included a family.

Video footage showed a shell slamming into a city street, not far from a bridge used by people fleeing the fighting. A group of fighters could be seen trying to help the family.

The handful of residents who managed to flee Mariupol before the humanitarian corridor closed said the city of 430,000 had been devastated.

“We saw everything: houses burning, all the people sitting in basements,” said Yelena Zamay, who fled to one of the self-proclaimed republics in eastern Ukraine held by pro-Russian separatists. “No communication, no water, no gas, no light, no water. There was nothing.”

British military officials compared Russia’s tactics to those Moscow used in Chechnya and Syria, where surrounded cities were pulverized by airstrikes and artillery.

Zelenskyy reiterated a request for foreign protectors to impose a no-fly zone over Ukraine, which NATO so far has ruled out because of concerns such an action would lead to a far wider war.

“The world is strong enough to close our skies,” Zelenskyy said Sunday in a video address.

Ukraine’s military is greatly outmatched by Russia’s, but its professional and volunteer forces have fought back with fierce tenacity. In Kyiv, volunteers lined up Saturday to join the military.

The West has broadly backed Ukraine, offering aid and weapon shipments and slapping Russia with vast sanctions. But no NATO troops have been sent to Ukraine.

Ukraine is planning to create an international legion of volunteer fighters from dozens of countries. More than 20,000 people have volunteered, according to Ukrainian Foreign Minister Dmytro Kuleba, though it was not clear how many were in Ukraine.

“The whole world today is on Ukraine’s side, not only in words but in deeds,” he said on Ukrainian television Sunday night.

Russia has made significant advances in southern Ukraine as it seeks to block access to the Sea of Azov. Capturing Mariupol could allow Moscow to establish a land corridor to Crimea, which Russia annexed from Ukraine in 2014 in a move that most other countries considered illegal.

Russia has become increasingly isolated in the days since the invasion began, closing itself off to outside sources of information as sanctions bite deeply into its economy. The ruble has plunged in value, and dozens of multinational companies ended or dramatically scaled back their work in the country.

On Sunday, American Express announced it would suspend operations in Russia, as well as in Russian-allied Belarus. Also, two of the so-called Big Four accounting firms, KPMG and PricewaterhouseCoopers, said Sunday they would end their relationships with their Russia-based member firms.

TikTok announced Sunday Russian users would not be able to post new videos or see videos shared from elsewhere in the world. The company blamed Moscow’s new “fake news” law, which makes it illegal, among other things, to describe the fighting as an invasion. Netflix also cut its service to Russia but provided no details.

Facebook and Twitter have already been blocked in Russia, along with access to the websites of a number of major international media outlets. TikTok is part of the Chinese tech company ByteDance.

U.S. House Speaker Nancy Pelosi said Congress is exploring how to further isolate Russia from the global economy, including banning the import of its oil and energy products into the United States. Pelosi said Sunday that the legislation under consideration would also repeal normal trade relations with Russia and Belarus and begin the process of denying Russia access to the World Trade Organization.

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Story: Yuras Karmanau. Associated Press reporters from around the world contributed to this report.

KYIV, Ukraine (AP) — Russian forces shelled Europe’s largest nuclear plant early Friday, sparking a fire as they pressed their attack on a crucial energy-producing Ukrainian city and gained ground in their bid to cut off the country from the sea.

The world’s leading nuclear authorities were concerned — but not panicked — about the damage to the power station, but the assault triggered a phone call between U.S. President Joe Biden and Ukrainian President Volodymyr Zelenskyy, and the U.S. Department of Energy activated its nuclear incident response team as a precaution.

The attack on the eastern city of Enerhodar and its Zaporizhzhia nuclear plant unfolded as the invasion entered its second week and another round of talks between the two sides yielded a tentative agreement to set up safe corridors to evacuate citizens and deliver humanitarian aid.

Nuclear plant spokesman Andriy Tuz told Ukrainian television that shells were falling directly on the facility and had set fire to one of its six reactors. That reactor is under renovation and not operating, but there is nuclear fuel inside, he said.

Firefighters cannot get near the flames because they are being shot at, he said, and Ukrainian Foreign Minister Dmytro Kuleba tweeted a plea to the Russians to stop the assault and allow fire teams inside.

“We demand that they stop the heavy weapons fire,” Tuz said in a video statement. “There is a real threat of nuclear danger in the biggest atomic energy station in Europe.”

The assault renewed fears that the invasion could damage one of Ukraine’s 15 nuclear reactors and trigger another emergency like the 1986 Chernobyl accident, the world’s worst nuclear disaster, which happened about 110 kilometers (65 miles) north of the capital.

U.S. Energy Secretary Jennifer Granholm tweeted that the Zaporizhzhia plant’s reactors were protected by robust containment structures and were being safely shut down.

In an emotional speech in the middle of the night, Zelenskyy said he feared an explosion that would be “the end for everyone. The end for Europe. The evacuation of Europe.”

“Only urgent action by Europe can stop the Russian troops,” he said. “Do not allow the death of Europe from a catastrophe at a nuclear power station.”

But most experts saw nothing to indicate an impending disaster.

The International Atomic Energy Agency said the fire had not affected essential equipment and that Ukraine’s nuclear regulator reported no change in radiation levels. The American Nuclear Society concurred, saying that the latest radiation levels remained within natural background levels.

“The real threat to Ukrainian lives continues to be the violent invasion and bombing of their country,” the group said in a statement.

Jon Wolfsthal, who served during the Obama administration as the senior director for arms control and nonproliferation at the National Security Council, said the plant’s reactors have thick concrete containment domes that should protect them from tank and artillery fire.

But he too was concerned about a potential loss of power at the plant, which could imperil its ability to keep the nuclear fuel cool.

The mayor of Enerhodar said earlier that Ukrainian forces were battling Russian troops on the city’s outskirts. Video showed flames and black smoke rising above the city of more than 50,000, with people streaming past wrecked cars, just a day after the U.N. atomic watchdog agency expressed grave concern that the fighting could cause accidental damage to Ukraine’s 15 nuclear reactors.

Prior to the shelling, the Ukrainian state atomic energy company reported that a Russian military column was heading toward the nuclear plant. Loud shots and rocket fire were heard late Thursday.

“Many young men in athletic clothes and armed with Kalashnikovs have come into the city. They are breaking down doors and trying to get into the apartments of local residents,” the statement from Energoatom said.

Later, a live streamed security camera linked from the homepage of the Zaporizhzhia plant showed what appeared to be armored vehicles rolling into the facility’s parking lot and shining spotlights on the building where the camera was mounted.

Then there were what appeared to be muzzle flashes from vehicles, followed by nearly simultaneous explosions in surrounding buildings. Smoke rose into the frame and drifted away.

Vladimir Putin’s forces have brought their superior firepower to bear over the past few days, launching hundreds of missiles and artillery attacks on cities and other sites around the country and making significant gains in the south.

Ukrainian Prime Minister Denys Shmyhal called on the West to close the skies over the country’s nuclear plants. “It is a question of the security of the whole world!” he said in a statement.

The U.S. and NATO allies have ruled out creating a no-fly zone since the move would pit Russian and Western military forces against each other.

Elsewhere, the Russians announced the capture of the southern city of Kherson, a vital Black Sea port of 280,000, and local Ukrainian officials confirmed the takeover of the government headquarters there, making it the first major city to fall since the invasion began a week ago.

Heavy fighting continued on the outskirts of another strategic port, Mariupol, on the Azov Sea. The battles have knocked out the city’s electricity, heat and water systems, as well as most phone service, officials said. Food deliveries to the city were also cut.

Associated Press video from the port city shows the assault lighting up the darkening sky above largely deserted streets and medical teams treating civilians, including one inside a clinic who appeared to be a child. Doctors were unable to save the person.

Severing Ukraine’s access to the Black and Azov seas would deal a crippling blow to its economy and allow Russia to build a land corridor to Crimea, seized by Moscow in 2014.

Overall, the outnumbered, outgunned Ukrainians have put up stiff resistance, staving off the swift victory that Russia appeared to have expected. But a senior U.S. defense official, speaking on condition of anonymity, said Russia’s seizure of Crimea gave it a logistical advantage in that part of the country, with shorter supply lines that smoothed the offensive there.

Ukrainian leaders called on the people to defend their homeland by cutting down trees, erecting barricades in the cities and attacking enemy columns from the rear. In recent days, authorities have issued weapons to civilians and taught them how to make Molotov cocktails.

“Total resistance. … This is our Ukrainian trump card, and this is what we can do best in the world,” Oleksiy Arestovich, an aide to Zelenskyy, said in a video message, recalling guerrilla actions in Nazi-occupied Ukraine during World War II.

The second round of talks between Ukrainian and Russian delegations was held in neighboring Belarus. But the two sides appeared far apart going into the meeting, and Putin warned Ukraine that it must quickly accept the Kremlin’s demand for its “demilitarization” and declare itself neutral, renouncing its bid to join NATO.

Putin told French President Emmanuel Macron he was determined to press on with his attack “until the end,” according to Macron’s office.

The two sides said that they tentatively agreed to allow cease-fires in areas designated safe corridors, and that they would seek to work out the necessary details quickly. A Zelenskyy adviser also said a third round of talks will be held early next week.

Despite a profusion of evidence of civilian casualties and destruction of property by the Russian military, Putin decried what he called an “anti-Russian disinformation campaign” and insisted that Moscow uses “only precision weapons to exclusively destroy military infrastructure.”

Putin claimed that the Russian military had already offered safe corridors for civilians to flee, but he asserted without evidence that Ukrainian “neo-Nazis” were preventing people from leaving and were using them as human shields.

He also hailed Russian soldiers as heroes in a video call with members of Russia’s Security Council, and ordered additional payments to families of men killed or wounded.

The Pentagon set up a direct communication link to Russia’s Ministry of Defense earlier this week to avoid the possibility of a miscalculation sparking conflict between Moscow and Washington, according to a U.S. defense official who spoke on condition of anonymity because the link had not been announced.

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Story: Jim Heintz, Yuras Karmanau and Mstyslav Chernov. Karmanau reported from Lviv, Ukraine; Chernov from Mariupol, Ukraine. Sergei Grits in Odesa, Ukraine; Francesca Ebel, Josef Federman and Andrew Drake in Kyiv; Jamey Keaten in Geneva; Lynn Berry, Robert Burns and Eric Tucker in Washington; Edith M. Lederer and Jennifer Peltz at the United Nations; and other AP journalists from around the world contributed to this report.

KYIV, Ukraine (AP) — The number of people sent fleeing Ukraine by Russia’s invasion topped 1 million on Wednesday, the swiftest refugee exodus this century, the United Nations said, as Russian forces kept up their bombardment of the country’s second-biggest city, Kharkiv, and laid siege to two strategic seaports.

The tally from the U.N. refugee agency released to The Associated Press amounts to more than 2% of Ukraine’s population being forced out of the country in less than a week. The mass evacuation could be seen in Kharkiv, where residents desperate to get away from falling shells and bombs crowded the city’s train station and tried to press onto trains, not always knowing where they were headed.

In a videotaped address, Ukrainian President Volodymyr Zelenskyy called on Ukrainians to keep up the resistance. He vowed that the invaders would have “not one quiet moment” and described Russian soldiers as “confused children who have been used.”

Moscow’s isolation deepened when most of the world lined up against it at the United Nations to demand it withdraw from Ukraine. And the prosecutor for the International Criminal Court opened an investigation into possible war crimes.

With fighting going on on multiple fronts across the country, Britain’s Defense Ministry said Mariupol, a large city on the Azov Sea, was encircled by Russian forces, while the status of another vital port, Kherson, a Black Sea shipbuilding city of 280,000, remained unclear.

Russian President Vladimir Putin’s forces claimed to have taken complete control of Kherson, which would make it the biggest city to fall yet in the invasion. A senior U.S. defense official disputed that.

“Our view is that Kherson is very much a contested city,” the official said, speaking on condition of anonymity.

Zelenskyy’s office told the AP that it could not comment on the situation in Kherson while the fighting was still going on.

The mayor of Kherson, Igor Kolykhaev, said Russian soldiers were in the city and came to the city administration building. He said he asked them not to shoot civilians and to allow crews to gather up the bodies from the streets.

“We don’t have any Ukrainian forces in the city, only civilians and people here who want to LIVE,” he said in a statement later posted on Facebook.

The mayor said Kherson would maintain a strict 8 p.m.-to-6 a.m. curfew and restrict traffic into the city to food and medicine deliveries. The city will also require pedestrians to walk in groups no larger than two, obey commands to stop and not to “provoke the troops.”

“The flag flying over us is Ukrainian,” he wrote. “And for it to stay that way, these demands must be observed.”

Mariupol Mayor Vadym Boychenko said the attacks there had been relentless.

“We cannot even take the wounded from the streets, from houses and apartments today, since the shelling does not stop,” he was quoted by the Interfax news agency as saying.

Russia reported its military casualties for the first time since the invasion began last week, saying nearly 500 of its troops have been killed and almost 1,600 wounded. Ukraine did not disclose its own military losses but said more than 2,000 civilians have died, a claim that could not be independently verified.

In a video address to the nation early Thursday, Zelenskyy praised his country’s resistance.

“We are a people who in a week have destroyed the plans of the enemy,” he said. “They will have no peace here. They will have no food. They will have here not one quiet moment.”

He said the fighting is taking a toll on the morale of Russian soldiers, who “go into grocery stores and try to find something to eat.”

“These are not warriors of a superpower,” he said. “These are confused children who have been used.”

Meanwhile, the senior U.S. defense official said an immense column of hundreds of tanks and other vehicles appeared to be stalled roughly 25 kilometers (16 miles) from Kyiv and had made no real progress in the last couple of days.

The convoy, which earlier in the week had seemed poised to launch an assault on the capital, has been plagued with fuel and food shortages, the official said.

On the far edges of Kyiv, volunteers well into their 60s manned a checkpoint to try to block the Russian advance.

“In my old age, I had to take up arms,” said Andrey Goncharuk, 68. He said the fighters needed more weapons, but “we’ll kill the enemy and take their weapons.”

Around Ukraine, others crowded into train stations, carrying children wrapped in blankets and dragging wheeled suitcases into new lives as refugees.

In an email, U.N. refugee agency spokesperson Joung-ah Ghedini-Williams told the AP that the latest data indicates the refugee count surpassed 1 million as of midnight in central Europe, based on figures collected by national authorities.

Shabia Mantoo, another spokesperson for the agency, said that “at this rate” the exodus from Ukraine could make it the source of “the biggest refugee crisis this century.”

A large explosion shook central Kyiv on Wednesday night in what the president’s office said was a missile strike near the capital city’s southern railway station. There was no immediate word on any deaths or injuries.

Russian forces pounded Kharkiv, Ukraine’s biggest city after Kyiv, with about 1.5 million people, in another round of aerial attacks that shattered buildings and lit up the skyline with flames. At least 21 people were killed over the past day, said Oleg Sinehubov, head of the Kharkiv regional administration.

Several Russian planes were shot down over Kharkiv, according to Oleksiy Arestovich, a top adviser to Zelenskyy.

“Kharkiv today is the Stalingrad of the 21st century,” Arestovich said, invoking what is considered one of the most heroic episodes in Russian history, the five-month defense of the city from the Nazis during World War II.

From his basement bunker, Kharkiv Mayor Igor Terekhov told the BBC: “The city is united and we shall stand fast.’’

Russian attacks, many with missiles, blew the roof off Kharkiv’s five-story regional police building and set the top floor on fire, and also hit the intelligence headquarters and a university building, according to officials and videos and photos released by Ukraine’s State Emergency Service. Officials said residential buildings were also hit, but gave no details.

The head of the U.N. nuclear watchdog agency warned that the fighting poses a danger to Ukraine’s 15 nuclear reactors.

Rafael Grossi of the International Atomic Energy Agency noted that the war is “the first time a military conflict is happening amid the facilities of a large, established nuclear power program,” and he said he is “gravely concerned.”

Russia already has seized control of the decommissioned Chernobyl power plant, the scene in 1986 of the world’s worst nuclear disaster.

In New York, the U.N. General Assembly voted to demand that Russia stop its offensive and immediately withdraw all troops, with world powers and tiny island states alike condemning Moscow. The vote was 141 to 5, with 35 abstentions.

Assembly resolutions aren’t legally binding but can reflect and influence world opinion.

The vote came after the 193-member assembly convened its first emergency session since 1997. The only countries to vote with Russia were Belarus, Syria, North Korea and Eritrea. Cuba spoke in Moscow’s defense but ultimately abstained.

Ukraine’s U.N. Ambassador Sergiy Kyslytsya said Russian forces “have come to the Ukrainian soil, not only to kill some of us … they have come to deprive Ukraine of the very right to exist.” He added: ”The crimes are so barbaric that it is difficult to comprehend.”

Russia ramped up its rhetoric. Foreign Minister Sergei Lavrov reminded the world about the country’s vast nuclear arsenal when he said in an interview with Al-Jazeera that “a third world war could only be nuclear.”

In the northern city of Chernihiv, two cruise missiles hit a hospital, according to the Ukrainian UNIAN news agency, which quoted the health administration chief, Serhiy Pivovar, as saying authorities were working to determine the casualty toll.

In other developments:

— A second round of talks aimed at ending the fighting was expected Thursday, but there appeared to be little common ground between the two sides.

— The price of oil continued to soar, reaching $112 per barrel, the highest since 2014.

— Russia found itself even more isolated economically as Airbus and Boeing said they would cut off spare parts and technical support to the country’s airlines, a major blow. Airbus and Boeing jets account for the vast majority or Russia’s passenger fleet.

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Story: Jim Heintz, Yuras Karmanau, Vladimir Isachenkov and Dasha Litvinova. Isachenkov and Litvinova reported from Moscow; Karmanau reported from Lviv, Ukraine. Mstyslav Chernov in Mariupol, Ukraine; Sergei Grits in Odesa, Ukraine; Francesca Ebel, Josef Federman and Andrew Drake in Kyiv; Jamey Keaten in Geneva; Lynn Berry, Robert Burns and Eric Tucker in Washington; Edith M. Lederer and Jennifer Peltz at the United Nations; and other AP journalists from around the world contributed to this report.