Abdullah al-Senussi, wanted former spymaster of slain Libyan dictator Moamer Kadhafi, was arrested in Mauritania overnight, prompting calls for his extradition Saturday by both Libya and France.
The former Libyan intelligence chief, who is also sought by the International Criminal Court, was arrested at Nouakchott airport after arriving on a regular flight from Casablanca in Morocco, a Mauritanian security source said.
Senussi, 62, who was travelling with a fake Malian passport, was taken to the national intelligence agency's office in Nouakchott, but it was unclear at this stage what the Mauritanian government planned to do with him, the source added.
Libyan government spokesman Salal al-Manaa said Tripoli wanted Senussi extradited "to give him a fair trial in Libya."
He said the former spymaster was accompanied at the time of his arrest "by someone who is believed to be his son."
French President Nicolas Sarkozy hailed the arrest and will seek his extradition to France, his office said.
Senussi faced an international arrest warrant after a Paris court sentenced him in absentia to life for his alleged involvement in an attack on a French airliner in 1989 that killed 170 people, a statement from the Elysee said.
The statement said Senussi's arrest was "the result of joint efforts by the French and Mauritanian authorities, of which the Libyan authorities were kept informed."
It said Paris would file a request to Nouakchott for Senussi to be held pending extradition within hours.
Senussi, a brother-in-law of Kadhafi, is wanted by The Hague-based International Criminal Court for what it alleges was his "crucial" role in trying to crush the country's popular revolt last year.
The ICC, which issued an arrest warrent for him on June 27, says Senussi was an "indirect perpetrator of crimes against humanity of murder and persecution based on political grounds" committed in Benghazi.
The court had not officially received information of his arrest, ICC spokesman Fadi al-Abdallah told AFP on Saturday.
"We are going to ask the Mauritanian authorities for official confirmation, and if that is the case seek their cooperation for handing the suspect to the court," he said.
Abdallah said Mauritania was not a party to the treaty that set up the court, "but like all UN member states it has been asked by the Security Council to cooperate with the ICC."
Senussi could also be held accountable in Libya for the Abu Salim prison massacre of 1996 when more than 1,000 detainees were gunned down.
The capture of the spy chief, a heavy-set man with a thick jawline and bushy black eyebrows, comes after he spent several months on the run.
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 announced his arrest but it was not confirmed and no pictures of Senussi have been released since then.
Long considered Kadhafi's right-hand man, Senussi remained faithful to the end to the man who ruled Libya with an iron fist for 42 years.
On August 21, the day rebels stormed Tripoli, Senussi made a rare appearance at the Rixos Hotel, headquarters of the foreign media in the Libyan capital, to denounce NATO's bombing campaign.
He said the military alliance, which bombed his Tripoli home a few days earlier, worked with Western intelligence and Al-Qaeda "to destroy Libya."
"Libya will not be ruled by bands of terrorists," Senussi said at the time.