Mudawi Ibrahim Adam, who spent his sixth day in detention yesterday, has been charged with espionage, which carries a potential death penalty, the Sudanese government's human rights advisory council said yesterday.
Dr Mudawi, chairman of the Sudan Social Development Organisation (Sudo), was initially held in a general detention centre after being arrested in a Khartoum street hours before he was due to fly to Ireland.
However, he has now been transferred to the custody of the country's attorney general and charged with espionage against the state. The crime carries the death penalty or life imprisonment.
He also faces a second charge of entering and photographing military areas and works.
Dr Mudawi was arrested with his driver and a Sudo photographer. The driver was released on Wednesday but the photographer, Yasir Saleem, remains in custody facing the same charges as Dr Mudawi.
Security officers raided Dr Mudawi's place of work on Thursday, seizing computers.
It is barely two months since he was released from his last period of captivity, when he was held in a "ghost house", the notorious network of private residences used as detention centres and torture chambers in Khartoum. - Rob Crilly in Nairobi