The son of a prominent Sudanese opposition leader says his father was detained after urging the country's president to surrender to an international court to face charges of genocide in Darfur.
Siddique Turabi says security agents came to the family's home late Wednesday and asked Hassan Turabi to come with them.
The 75-year old leader's whereabouts remain unknown.
The dissident had said President Omar al-Bashir should give himself up to the Hague-based International Criminal Court.
The ICC prosecutor has asked for an arrest warrant against al-Bashir. A decision is expected soon.
Once an ally of al-Bashir, Turabi fell out with the president and now heads the main opposition party.