Sudan released an Islamist opposition leader on Monday, two months after he was detained for calling on President Omar Hassan Al-Beshir 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 said. Turabi, leader of the Islamist Popular Congress Party and a central figure in Sudan for decades, was the spiritual mentor behind Al-Beshir's government when it took power in a 1989 coup. In January, Turabi became the only political leader inside Sudan to call on Beshir to hand himself in to the Hague-based International Criminal Court (ICC) to face charges of orchestrating war crimes in the western Darfur region. Siddig said his father appeared in good health but had lost weight. Turabi, Al-Beshir'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. 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.