KHARTOUM (Reuters) - Sudan released an Islamist opposition leader on Monday, two months after he was detained for calling on President Omar Hassan Al-Bashir to surrender to the International Criminal Court, his family said.

Hassan al-Turabi, 76, was freed from prison in Port Sudan and flown to his home in the capital Khartoum in the early hours without explanation, his son Siddig told Reuters.

We don't know what is going to happen in the morning but there is no guard outside the house in Khartoum. He has been released ... We are very happy, said Siddig.

In January, Turabi became the only political leader inside Sudan to call on Bashir to hand himself in to the Hague-based International Criminal Court (ICC) to face charges of orchestrating war crimes in the western Darfur region.

Turabi, Bashir's close political and religious ally until they split in a bitter power struggle in 1999-2000, said the president should do this to save Sudan from the sanctions and political turmoil that would follow if he defied the court.

Last week, the ICC issued an arrest warrant for Bashir but he has repeatedly said he would defy the court, which is not recognised by the Sudanese government.

Most other opposition figures in Sudan have said little about the case or rallied round the president, describing the ICC's charges as a Western and Zionist plot against Sudan.

SPIRITUAL LEADER

Turabi, leader of the Islamist Popular Congress Party and a central figure in Sudan for decades, was the spiritual mentor behind Bashir's government when it took power in a 1989 coup.

In the 1990s when Sudan hosted al Qaeda leader Osama bin Laden, Turabi was widely seen as the driving force behind Khartoum's promotion of militant Islamist groups.

Siddig said his father appeared in good health but had lost weight.

Bashir Adam Rahman, secretary for international affairs in Turabi's party, was also released, Siddig said.

On Sunday, Bashir -- brandishing a sword at a rally in Darfur -- threatened to expel diplomats and more aid groups.

Sudan has already closed 13 foreign and three local aid groups saying they had helped the ICC.

We will expel anyone who goes against Sudanese law, whether they are voluntary organisations, diplomatic missions or security forces, said Bashir.

Before the expulsions, the United Nations and aid groups were running the world's largest humanitarian operation in Darfur.

International experts say almost six years of conflict in Darfur have killed 200,000 people and displaced more than 2.7 million people from their homes.

(Editing by Ralph Gowling)

Sudan