Seif al-Islam was "arrested in southern Libya" by former rebel forces, NTC justice minister
Mohammed al-Allagui told the AFP news agency Saturday. That followed an announcement by operations chief Bashir Taib in Zintan, south-west of Tripoli, that his
fighters had arrested Seif along with three aides in the Ubari region of southern Libya.
He was reported to have been unharmed at the time of his capture, although photos show him later with an injured hand, and to have been flown to Zintan, where an angry crowd awaited the plane.
The news was greeted with enthusiasm on the streets of Tripoli.
Al-Senussi is still at large.
Earlier he was reported to be trying to escape to Niger but may have been trying to organise a return to power and armed resistance to the NTC.
The NTC is expected to name a new government on Sunday.