Libya has confirmed that Muammar Gaddafi's intelligence chief Abdullah Senussi was arrested in Mauritania, government spokesman Nasser al-Manee said.
"[Senussi] was arrested this morning in Nouakchott airport and there was a young man with him. We think it is his son," Manee told a news conference on Saturday, adding that he was carrying a passport from Mali.
"Calls are under way by Libyan authorities to request his extradition," Manee said.
The government "is ready to receive Abdullah Senussi and to detain him in a Libyan prison and to give him a fair trial in Libya," he added.
Al Jazeera's Mohammed Fadel, reporting from the Mauritanian capital Nouakchott, said Senussi arrived on an Air Morocco flight from Casablanca on a forged Malian passport and is now under police interrogation in Mauritania.
"In a short, brief statement, the authorities did not give any more information on Senussi. No one knows exactly how the authorities are going to co-operate with Libya or the ICC [International Criminal Court], mostly because Senussi has not been charged with any crime in Mauritania," our correspondent said.
Senussi was the right-hand man and brother-in-law of Gaddafi, who was deposed from power and eventually killed in a nine-month uprising against his decades-long rule last year.
The 62-year-old spy chief, along with Gaddafi and his son Saif al-Islam, was indicted on suspicion of war crimes by the International Criminal Court last June and his whereabouts has been unknown since Tripoli, Libya’s capital, fell to rebel forces last August.
The ICC indictment accuses Senussi of being an "indirect perpetrator of crimes against humanity of murder and persecution based on political grounds" committed in the eastern city and rebel stronghold of Benghazi.
Al Jazeera's Nicole Johnston, reporting from Tripoli, said Libya's National Transitional Council (NTC) had made an official request to Mauritania to have him deported back to Libya.
"They want him to face Libyan justice in Tripoli. [The NTC] has not heard back, and it should be pointed out that Mauritania is not a signatory to [ICC extradition laws]," our correspondent said.
"For some 40 years he was leader of intelligence forces here in Libya, and one thing he is known for is the massacre of some 1,200 political prisoners in Abu Salim prison."
Security sources in Niger and Mali said in October that Senussi and several of his men passed through their territory.
A month later, Libya's new government erroneously announced his arrest but no pictures of Senussi have been released since then.
Senussi was also one of six Libyans convicted in absentia and sentenced to life in prison in France for the 1989 bombing of a French passenger over Niger that killed all 170 people on board.
The French government had previously asked that he be handed over to France.