JOHANNESBURG — South Africa’s main opposition party on Monday tried to block a government plan to withdraw from the International Criminal Court, saying the move is illegal and that the country’s top court should intervene.

The government acted unconstitutionally because it announced plans to withdraw from the human rights tribunal based in The Hague, Netherlands, without consulting the South African parliament, the Democratic Alliance party said in an affidavit asking the Constitutional Court to hear its case. It described the government move as hasty and “procedurally irrational.”

South Africa has said a withdrawal bill will soon go to parliament, where the ruling African National Congress party has a majority and is likely to approve the measure.

Last week, South Africa notified the United Nations that it will withdraw from the treaty that created the International Criminal Court, alarming international human rights groups and raising fears of an African exodus from the court, which has more than 120 member states. Some African countries have argued that the court has unfairly targeted their continent and that they are strengthening their own institutions to deal with threats to human rights.

U.N. Secretary-General Ban Ki-moon regretted South Africa’s decision to withdraw from the ICC and expressed the hope that the government will reconsider it, according to a statement released Monday by his spokesman. Ban recalled that South Africa had played a “significant role” in the establishment of the ICC and was one of the first signatories to the pact setting up the court.

“The Secretary-General believes that the International Criminal Court is central to global efforts to end impunity and prevent conflict,” the statement said. Ban added that countries can seek to resolve concerns regarding the functioning of the court through the Assembly of States Parties, the ICC’s oversight board.

Richard Dicker, international justice director at Human Rights Watch, also urged South Africa to reconsider its withdrawal decision.

“South Africa has made a profoundly negative decision for victims and the rule of law,” Dicker said.

Also last week, President Pierre Nkurunziza of Burundi signed legislation to withdraw from the ICC, which had said it would investigate political violence that followed Nkurunziza’s decision last year to pursue a third term, which some have called unconstitutional.

The head of the ICC’s oversight board, Senegal’s Justice Minister Sidiki Kaba, urged South Africa and Burundi to abandon their decision to withdraw from the ICC.

Kaba acknowledged criticism that the court mostly prosecutes African nationals, adding “But we must also remember that these are African states that have applied to the court.”

“We must seize this opportunity to engage in dialogue,” said Kaba, adding that member states could work through the oversight board to discuss changes issues they have with the court.

Uganda has said the issue of whether African nations should withdraw as a group is likely to be raised at an African Union meeting in Ethiopia in January. But Nkosazana Dlamini-Zuma, chair of the African Union commission chair, said Monday that it is a “purely sovereign decision for each country to join or pull out.”

Speaking in South Africa, Dlamini-Zuma cited the trial of Chad’s former president, Hissene Habre, as an example that Africa has the capacity to prosecute its own leaders, reported News24, a South African media organization. In May, a court in Senegal known as the Extraordinary African Chambers, set up by the African Union, found Habre guilty of torture, mass killing, war crimes and other violations and sentenced him to life in prison.

“The ICC is the court of last instance. The first instance is national courts. They must be strengthened so that they can deal with situations as they arise,” Dlamini-Zuma said, according to News24.

Under the Rome Statute that created the International Criminal Court, signatory countries have a legal obligation to arrest anyone sought by the tribunal. South Africa said the treaty contradicts South Africa’s diplomatic immunity law and prevents the country from acting as a regional peacemaker, a role that could require it to host adversaries on its own soil.

South Africa’s withdrawal announcement followed a dispute last year over a visit by Sudanese President Omar al-Bashir, who is wanted by the ICC for alleged war crimes, crimes against humanity and genocide in Darfur. Al-Bashir was allowed to leave South Africa even though a local court ordered authorities to stop him.

Story: Christopher Torchia