Former Libyan rebels angry over unpaid stipends opened fire on the headquarters of the interim government on Tuesday after surrounding the building.

"Many men encircled the building and opened fire against it with weapons including anti-aircraft cannons," a government employee present during the attack told AFP.

There was no immediate report of casualties.

Several trucks mounted with anti-aircraft guns surrounded the building in central Tripoli, blocking traffic, witnesses said.

Government spokesman Nasser al-Manaa said the defence minister was negotiating with the fighters, who "came in protest over (unpaid) stipends," referring to a reward scheme for those who fought against Moamer Kadhafi's regime in 2011.