Mauritanian authorities arrested Muammar Gaddafi's chief of intelligence and right-hand man Abdullah al-Senussi as he entered the country on a false passport, Mauritania's state news agency said on Saturday.

Senussi, who for decades before the late dictator's fall inspired fear and hatred in ordinary Libyans, is sought by the Hague-based International Criminal Court on charges of crimes against humanity. If confirmed, his arrest will put an end to months of uncertainty over his whereabouts.

Official Mauritanian agency AMI said Senussi was arrested late on Friday as he arrived at the airport in the West African state's capital Nouakchott on a regular flight from Casablanca in Morocco. It said he was bearing a falsified Malian passport.

Mauritania has not signed the Rome Statute governing the ICC and authorities were not immediately available to confirm the arrest or comment on what they would do with Senussi, the last significant former Gaddafi regime figure still at large.

ICC spokesman Fadi El-Abdallah said he was aware of reports of 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 in a statement. Mauritania is not a state party (to the Rome treaty), but has been, like all U.N. members, urged by the UNSC (the U.N. Security Council) to cooperate with the ICC.

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 Senussi and Gaddafi's son Saif al-Islam as being indirect co-perpetrators of murder and persecution.

Saif al-Islam was captured disguised as a Bedouin in the Sahara in November is awaiting trial in Libya on rape and murder charges. Libya's National Transitional Council says he will get a fair hearing but his supporters want him sent to the Hague.

Mauritanian President Mohamed Ould Abdel Aziz, an army general who was toppled his predecessor in a 2008 coup, won election in a 2009 vote decried by rivals as rigged.

Yet France has hailed him as a key partner and he went on to play a leading role in the awkward African diplomacy over Libya that finally led to the continent recognising the National Transitional Council as its new leaders.

The case of Senussi may revive interest in international incidents long shrouded in mystery, from the days in the 1980s and 90s when Gaddafi's Libya waged undercover war on the West.

Senussi's name has been linked with the Lockerbie bombing of 1988, while France has said it wants to try Senussi over a 1989 airliner bombing over Niger that killed 170 people including 54 French nationals.

(Reporting by Laurent Prieur; Writing by Mark John; Editing by Giles Elgood)