The former Libyan intelligence chief Abdullah al-Senoussi, who was one of the most prominent figures in Muammar Gaddafi's regime and is wanted by the international criminal court for alleged crimes against humanity, has been detained, according to the Mauritanian government.

Al-Senoussi helped direct efforts to quash the rebellion against Gaddafi's rule last year, and the ICC has indicted him along with Gaddafi's son Saif al-Islam.

Mauritania's state information agency said Senoussi was arrested at the airport in the capital Nouakchott after arriving from the Moroccan city of Casablanca. It said he was carrying a fake Malian passport.

A spokesman for Libya's ruling National Transitional Council, Mohammed al-Hareiz, said the arrest was not yet confirmed.

As Gaddafi's regime crumbled in the second half of 2011, many of the dictator's inner circle reportedly fled from advancing rebels toward the Sahara, where the regime had long cultivated ties with desert groups both in Libya and in neighbouring countries.

Gaddafi's son Saif al-Islam was arrested in November by fighters in Libya's remote southern desert. He has been held largely without access to the outside world ever since and Libyan authorities say they want to put him on trial at home, despite an arrest warrant issued by the ICC.

Some Libyan officials reported at the time that Senoussi had also been captured and was being held in the southern city of Sabha. But some later cast doubt on that assertion, and his whereabouts have not been known – a reflection of the confusion in post-Gaddafi Libya, where "revolutionary militias" hold local control in many towns and cities with little accountability to the Tripoli government.

In October, a western diplomatic official in Mali's capital, Bamako, told the Associated Press that Senoussi was in Mali and that the French government was taking the lead in hunting him down. The official spoke on the condition of anonymity as he was not authorised to talk to the press.

Senoussi, Gaddafi's brother-in-law, 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 asked last year that he be handed over to France when captured.

Judges at the Netherlands-based ICC issued an arrest warrant for Senoussi last June on two counts of crimes against humanity – murder and persecution – for allegedly masterminding attacks on civilians in the early days of the uprising that eventually toppled Gaddafi from power.

If Senoussi is handed over to the Hague-based court, he would be the first suspect indicted for alleged atrocities in Libya to be taken into custody.

The court also indicted Gaddafi, the ousted leader was killed by rebel fighters in October. Libyan authorities say they want to put his son, Saif al-Islam, on trial at home instead of turning him over him to the court.