Saif al-Islam Gaddafi, second son of the late deposed Libyan leader Col Muammar Gaddafi, is said to have been freed under an amnesty, in a move which could fuel further instability.
His father’s preferred successor, he had been held by a militia in the town of Zintan for the past six years.
The Abu Bakr al-Siddiq Battalion said he had been released on Friday but he has not been shown in public.
A source has told the BBC he is in the Tobruk area of eastern Libya.
His lawyer, Khaled al-Zaidi, also said he had been released but would not say which city Saif al-Islam had travelled to for security reasonsThe Abu Bakr al-Siddiq Battalion said it was acting on a request from the “interim government”.
That government – based in the east of the country – had already offered amnesty to Saif al-Islam.
However, he has been sentenced to death in absentia by a court in Tripoli, the west of the country, where control is in the hands of the rival, UN-backed Government of National Accord.
Previous reports of Saif al-Islam Gaddafi’s release proved to be false.
He is wanted by the International Criminal Court for crimes against humanity during his father’s unsuccessful attempts to put down the rebellion.