Abdullah al-Senussi, former spymaster of Libya's slain dictator Moamer Kadhafi, was arrested in Mauritania, prompting calls Saturday for his extradition by Tripoli and Paris.
The former intelligence chief and right-hand man to Kadhafi was arrested at Nouakchott airport after arriving on a regular flight from Casablanca in Morocco, a Mauritanian security source said.
Senussi, 62, who is also wanted by the International Criminal Court (ICC), was travelling on a fake Malian passport. He was taken to the national intelligence agency's office, the source said.
Long feared in Libya, he is wanted in The Hague for crimes committed while trying to crush last year's uprising, while France has convicted him in absentia over the downing of an airliner that claimed 170 lives.
Mauritanian police said that before considering any extradition requests, they want to investigate him with Interpol. They did not say how long the investigation might take before the requests are examined.
Libyan government spokesman Salal al-Manaa said Tripoli wanted Senussi extradited "to give him a fair trial in Libya", and that the prosecutor general had sent an extradition request through Interpol.
Manaa 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 Senussi's extradition, his office said.
Senussi's arrest was "the result of joint efforts by the French and Mauritanian authorities, of which the Libyan authorities were kept informed", the statement added.
Senussi faced an international arrest warrant after a Paris court sentenced him in absentia to life for involvement in the downing of a French airliner in 1989 that killed 170 people, said the Elysee statement.
The UTA airliner on a flight from Brazzaville to Paris via N'Djamena was brought down by a bomb on September 19, 1989 in Niger.
This attack -- along with that a year earlier against a PanAm jumbo jet over Lockerbie, Scotland, in which 270 people were killed -- led to a UN-mandated air blockade of Libya in 1992.
British Foreign Secretary William Hague also welcomed Senussi's capture.
"Like others who have sought to evade justice, he must now be held to account for his actions and face trial on the charges brought against him," he said in a statement.
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He also called on Nouakchott to cooperate with the ICC.
Senussi, a brother-in-law of Kadhafi, is wanted by the ICC in The Hague for what it alleges was his "crucial" role in trying to crush the country's popular revolt last year.
The ICC issued an arrest warrant for Senussi on June 27, saying he was an "indirect perpetrator of crimes against humanity, of murder and persecution based on political grounds" committed in northeastern Benghazi.
ICC spokesman Fadi al-Abdallah told AFP on Saturday the court had not yet received official information of his arrest.
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," he added.
The families of victims of the UTA flight expressed satisfaction at the news.
"We have never lost hope of seeing those responsible for the attack put on trial," Guillaume Denoix de Saint Marc, their association's president, said in a statement.
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 spy chief, a heavy-set man with a thick jawline and bushy black eyebrows, spent several months on the run before his capture.
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 never ended up confirming it.
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 capital, to denounce NATO's bombing campaign.
He said the alliance, which had bombed his Tripoli home days earlier, worked with Western intelligence and Al-Qaeda "to destroy Libya", vowing defiantly: "Libya will not be ruled by bands of terrorists."