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

There were no immediate reports of casualties.

"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.

"Some men entered the premises and fired from inside," he said, adding that chaotic scenes unfolded as people sought cover.

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

Government spokesman Nasser Al Manaa said Defence Minister Osama Juili was negotiating with the fighters, who "came in protest over (unpaid) stipends".

Last month, citing widespread fraud, Libyan authorities halted the payment of cash bonuses to rebels who had fought against Muammar Gaddafi's regime in 2011.