Libya's former Prime Minister al-Baghdadi al-Mahmoudi has been extradited to Libya from Tunisia, where he had fled during the uprising against Col Muammar Gaddafi last year.
Mr Mahmoudi, 70, had served as prime minister from March 2006 but fled Libya when Col Gaddafi's forces lost control of Tripoli.
Mr Mahmoudi becomes the first senior official to be returned for trial.
He was arrested in Tunisia in September for illegal entry.
A sentence of six months imprisonment for that offence was overturned on appeal, but Mr Mahmoudi had remained in Tunisian custody following the extradition request from Libya.
Mr Mahmoudi was transferred by helicopter on Sunday.
Defence ministry official Mohammed al-Ahwal told Reuters: "Mahmoudi is now in Tripoli and we are holding him in a prison."
Human rights groups had asked Tunisia not to extradite him, saying he could be subject to rights violations.
Mr Mahmoudi's lawyers have expressed fears for his life, saying he now has sole knowledge of many of the state secrets from Gaddafi's time in power.
Libya's new government has pledged to treat all detainees fairly.
Tunisia's President Moncef Marzouki had promised earlier this year to hand over Mr Mahmoudi if he were guaranteed a fair trial, but in May he said he was in principle opposed to the move.
Agence France-Presse news agency quoted a Tunisian presidential source as saying that the decision had been taken by the country's government without consulting the presidency, suggesting the president had not signed an extradition decree.
A Tunisian government statement said the extradition did not require the president's signature. It said the decision to extradite had been made following a report by a Tunisian delegation to Tripoli, which found that the conditions for a fair judicial process had been met.
Libyan authorities have been involved in a tussle with the International Criminal Court over where Gaddafi's son, Saif al-Islam, should stand trial over his role in the uprising that ended his father's rule.
The Zintan militia that captured Saif al-Islam last November have since refused to hand him over to central authorities in Tripoli.
Col Gaddafi was killed by rebels after being captured and his corpse was put on public display.