Former Libyan intelligence chief Abdallah al-Senussi has been charged in Mauritania with illegally entering the country, officials say.
Mr Senussi, who fled Libya after the fall of Muammar Gaddafi, was held at Nouakchott airport after flying in from Morocco in March.
Both Libya and the International Criminal Court want him extradited to face trial for crimes against humanity.
Mauritanian officials say he faces trial for using false travel documents.
A judicial source told AFP news agency he had been placed in a specially prepared prison cell ahead of his trial.
The interim Libyan government has said it wants him back on Libyan soil so he can stand trial for numerous allegations of murder and human rights abuses while he was Gaddafi’s head of intelligence.
Nicknamed “the butcher”, Mr Senussi was Gaddafi’s brother-in-law and has been described as one of his closest aides.
He has been implicated in the massacre in 1996 of more than 1,000 inmates at the Abu Salim prison in Tripoli.
In March, soon after Mr Senussi’s arrest, Libya’s Deputy Prime Minister Mustafa Abushagur said Mauritania had agreed to hand him over. Mauritanian officials have said no decision has been made on his extradition.
Interpol has issued an international “red notice” call for his arrest at Libya’s request.
Mr Senussi is also wanted on a 2011 ICC arrest warrant in connection with the violent suppression of protests during last year’s Libyan uprising that toppled the late Col Gaddafi.
In addition, he is sought by the authorities in France after a court there sentenced him to life in prison for his involvement in a 1989 attack on a French plane that killed 170 people.BBC