Khartoum, Sudan ? Sudan freed a senior opposition leader Monday who was jailed after urging the president to face war crimes charges, an apparent attempt to show unity as the country defies an international order to bring its leader to trial over bloodshed in Darfur.

Hassan Turabi, an Islamist who helped bring President Omar al-Bashir to power but now is his top rival, is the only Sudanese politician who has dared say al-Bashir should surrender to an international court. Turabi was jailed for seven weeks, a move criticized both internationally and locally.

The government appears to be confident that freeing Turabi ensures his Popular National Congress Party will ultimately stand behind the president, even if Turabi doesn’t change his views.

At his home in Khartoum on Monday, Turabi criticized al-Bashir’s defiance of the Netherlands-based International Criminal Court and condemned the government’s expulsion of major foreign aid groups from Darfur in retaliation for the warrant.

He did not repeat his outright call for the president’s surrender. But asked whether he thought al-Bashir eventually would have to turn himself in, Turabi told The Associated Press: “It will take time, probably. … All human beings under pressure, of course, ultimately respond.”

The 76-year-old looked tired and slightly thinner, but flashed a wide smile as he greeted hundreds of well-wishers. His deteriorating health was a factor in his release, said his son, Siddique Turabi.

Al-Bashir has taken a tough stance in defiance of the ICC. The order expelling 13 aid groups has raised fears of a humanitarian crisis in Darfur, where millions rely on international help to survive. The president has threatened to throw out more aid groups, foreign diplomats and U.N. peacekeepers if they attempt to implement the warrant or work with the court. Al-Bashir has rejected any dealings with the tribunal.

The United Nations’ top aid official said Monday the world body would try to fill life-threatening gaps caused by the expulsions, but warned that U.N. agencies and aid groups still there don’t have the resources to take over all the work helping displaced people in Darfur.

John Holmes, the U.N. humanitarian chief, said Sudan’s government does not have the capacity to replace all the activities that have been going on. He said 7,610 people worked for the 13 affected aid groups, 308 international staff members and 7,302 Sudanese, representing more than half the roughly 14,000 humanitarian workers in Darfur.

The expulsion “is likely to have a major impact on millions of people in Darfur, in particular, who are in need on a daily basis of life-saving humanitarian assistance,” Holmes said.

In a visit Monday, the head of the African Union sharply criticized the ICC, saying the court was using Africa as a “laboratory” for Western countries’ ideas. He told reporters the warrant has undermined efforts at peace and reconciliation in Darfur and put African Union-United Nations peacekeepers there at risk.

“Enough with these people,” Jean Ping said angrily of the court.