Abdullah Al Senussi, Muammar Gaddafis much hated spy chief - seen here proclaiming victory for his leader just days before the fall of Tripoli last year.

The last significant old regime figure still-at-large was arrested in this airport in the West African state of Mauritania on Friday.

He was reportedly travelling with his son on a flight from Morocco, carrying a fake passport from Mali.

Gaddaffi's right hand man and brother-in-law, Senussi was indicted by the International Criminal Court for war crimes last year.

But Mauritania has not signed the statute governing the Netherlands-based war crimes court.

In Tripoli, Libyan government spokesman Nasser Al Manee said authorities were pressing for Senussi's extradition.

He said the prosecutor general had already sent an extradition request to Mauritania so he could stand trial in Libya.

News of Senussi's arrest was greeted with jubilation in Tripoli.

(SOUNDBITE) (Arabic) TRIPOLI CITIZEN, AL-AMORY ABDULAH, SAYING:

This is the happiest moment for Libyans I wished we had arrested him here. No matter how much we subject him to it will not be sufficient revenge for what Senussi did"

Senussi built up a reputation as one of Gaddafi's most brutal enforcers as chief of internal security in the 1980s.

Many Libyans also hold Senussi responsible for the mass killing of some 1200 inmates here at Tripioli's Abu Salim prison in 1996.

Sunita Rappai, Reuters