The Libyan authorities have confirmed the arrest in Mauritania of former Libyan leader Muammar Gaddafi's intelligence chief.
Mauritanian security officials say Abdullah al-Senussi was detained at Nouakchott airport after arriving on a regular flight from the Moroccan city of Casablanca on a false Malian passport.
Senussi, 63, was Gaddafi's brother-in-law, and has been described as one of his most trusted aides. He fled Libya when Gaddafi was ousted and killed last year.
The International Criminal Court issued a warrant for his arrest last year for crimes against humanity.
France says the arrest was carried out in a joint operation between French and Mauritanian authorities, and President Nicolas Sarkozy says he will request Senussi's extradition.
A French court convicted the former spy chief of involvement in a 1989 attack on a French plane that killed 170 people, and sentenced him to life in prison.
Libyan authorities, however, are also demanding his extradition. The ICC wants him tried in The Hague but the Libyan authorities say he will receive a fair trial at home.
Mauritania has not signed the ICC's statute, the BBC reports, and it is unclear what the country intends to do with Senussi.
Known as 'the butcher'
Analysts say he could provide the most detailed insights so far into the inner workings of the Gaddafi regime.
Senussi, nicknamed "the butcher", was one of the last significant members of the regime still at large.
Libyan, Arab and Western sources describe him as a thuggish figure who would beat and abuse prisoners.
He is thought to have been responsible for purges of opponents within the regime in the 1980s and 90s, and for the deaths of 1200 political prisoners at Tripoli's Abu Salim prison in 1996.
He kept a low public profile during last year's uprising, but reportedly played a key role in attempts to crush the revolt in the eastern city of Benghazi when it began last February.