Former Libyan leader Muammar Gaddafi’s intelligence chief Abdullah Al-Senussi has been arrested.
Libya confirmed Senussi had been arrested in Mauritania on Saturday. He was carrying a Malian passport.
Nasser al-Manee told a press conference: "He was arrested this morning in Nouakchott airport and there was a young man with him. We think it is his son."
Senussi, who is Gaddafi’s brother-in-law, fled Libya after he was ousted and killed last year.
He has been described as one of Gaddafi’s most trusted aides, the BBC reported.
The International Criminal Court issued a warrant for his arrest last year for crimes against humanity.
Libya has sent an extradition request to the Mauritanian government through Interpol, says Reuters.
A spokesman said: "The Libyan foreign ministry is in touch with Mauritania about the procedure. The Libyan government is ready to receive Abdullah Al-Senussi ... and give him a fair trial in Libya."
Foreign Secretary William Hague welcomed the arrest and said Senussi must face trial for his part in last year's brutal repression in Libya.
Senussi is also wanted in connection with the bombing of a French airliner in 1989.
Mr Hague said: "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.
"I congratulate the Mauritanian authorities for detaining him and encourage all involved to co-operate fully with the ICC (International Criminal Court) under UN Security Council Resolution 1970.
"The detention of the final Libya ICC indictee now offers the Libyan authorities the opportunity to focus fully on rebuilding their country and continuing the transition to democracy."
In a message clearly pointed at the Syrian regime, he added: "Al-Senussi's arrest is a further reminder that people at all levels should think carefully about the consequences of their actions - whether they are ordering attacks on civilians, carrying out such attacks or otherwise suppressing the wishes of people wanting a better future.
"The reach of justice is long and there will come a day when they are held to account."