An AFP reporter saw a smiling Mahdi, chief of the opposition Umma party, greeting about 200 noisy supporters at his party headquarters in Khartoum's twin city of Omdurman.
Minutes earlier State Minister of Information Yassir Yousef told AFP that Mahdi "has been released".
The National Intelligence and Security Service (NISS) arrested Mahdi on May 17 after he reportedly accused a counter-insurgency unit of abuses against civilians in the Darfur region.
Mahdi was charged with treason-related offences which can bring a death sentence upon conviction, but the status of those charges was not immediately clear today.
