Libya has confirmed that Muammar Gaddafi's intelligence chief Abdullah al-Senussi has been arrested in Mauritania.
Government spokesman Nasser al-Manee said he was arrested in Nouakchott airport, carrying a passport from Mali.
Mr Manee also said Libya has sent Mauritania an extradition request through Interpol.
Mr Senussi is sought by the Hague-based International Criminal Court on charges of crimes against humanity.
ICC spokesman Fadi El-Abdallah earlier said he was aware of reports of Mr Senussi's capture.
"We will ask the Mauritanian authorities for an official confirmation and in this eventuality, seek their cooperation for the surrender of the suspect to the court," he said.
"Mauritania is not a state party [to the Rome treaty], but has been, like all UN members, urged by the UNSC to co-operate with the ICC."
Mr Senussi is suspected of a key role in the killing of more than 1,200 inmates at Tripoli's Abu Salim prison in 1996.
It was the arrest of a lawyer for victims' relatives that sparked Libya's Arab Spring revolt in February last year.
The ICC has charged Mr Senussi and Gaddafi's son Saif al-Islam as being "indirect co-perpetrators" of murder and persecution.
