Amnesty International says a Sudanese rights activist from a conflict-torn area along the north-south border has been detained and the rights group fears he might be tortured.
Amnesty says Bushra Gamar Rahma was arrested at his home last week just outside the capital, Khartoum.
Friday's statement by the London-based group says authorities have refused to say where he is being held and have denied him access to family or a lawyer.
Rahma is originally from Southern Kordofan, where the north has recently launched a crackdown on rival black Nuba tribesmen.
Amnesty says it appears Rahma's arrest is related to the conflict as Southern Sudan prepares to declare independence from the north. The U.N. says the violence has displaced thousands.