Saadi Gaddafi had been let into Niger on humanitarian grounds and was due in its capital Niamey later, said Niger's Justice Minister Marou Amadou.

Col Gaddafi's whereabouts are unknown. He has said he will die in Libya.

Anti-Gaddafi troops now control most of Libya, including the capital Tripoli. Loyalists are holding out in several cities including Bani Walid and Sirte.

On September 11, anti-Gaddafi forces resumed their attack on Bani Walid, 180km (110 miles) from Tripoli, supported by Nato air strikes. Officials say their forces are now within reach of the centre of the town.

They also moved closer to the Mediterranean city of Sirte, Col Gaddafi's birthplace.