The spy chief has been accused of various human rights abuses.
Mauritania has handed over Abdullah al-Senussi, the former spy chief of late Libyan leader, Muammar Gaddafi, to Libya.
Mr. Senussi was declared wanted in Libya for crimes committed during his tenure.
“He was extradited to Libya on the basis of guarantees given by Libyan authorities,” Reuters quotes a Mauritanian government source, without giving details on the guarantees. State media also reportedly said Mr. Senussi had been extradited on Wednesday morning.
Libya’s foreign ministry said separately that it could not confirm the story but would welcome Mr. Senussi’s extradition.
The ex-spy chief is also wanted by the International Criminal Court (ICC) for the violent crackdown on protesters last year. He is also wanted by France in connection with an attack on an airline.
Months of wrangling over who would put him on trial delayed his transfer after Mauritania insisted he faced charges first for illegal entry into the country.
He was arrested in Mauritania after fleeing Libya as last year’s uprising toppled his former boss, Muammar Gaddafi.
He was later charged with illegally entering the country and using forged documents, and transferred to the civilian prison in Nouakchott.
In June 2011, the ICC issued a warrant for Mr. Senussi for crimes against humanity alleged to have been carried out in Benghazi, the main base of the Libyan opposition during the revolt last year.
France has already sentenced Mr. Senussi to life imprisonment for the shooting down of a UTA airliner over Niger in 1989 in which 170 people were killed.
He has been accused of various human rights abuses including his alleged role in the 1996 massacre of more than 1,000 inmates at the Abu Salim prison in Tripoli.