Forces backing Libya's UN-recognised government fought house-to-house battles with General Khalifa Haftar's Libyan National Army (LNA) in southern parts of the capital Tripoli on Sunday and appeared to be gaining ground.
Tripoli soldiers, some in jeans and t-shirts, took cover by abandoned buildings as they fired on LNA's positions. Some carried anti-aircraft guns they had had to remove from their trucks to get through the narrow streets.
The Libyan National Army, which is allied to a rival administration in eastern Libya, mounted an offensive on Tripoli three weeks ago but despite heavy fighting has failed to breach the city's southern defences.
The battle for the capital has all but wrecked U.N.-backed efforts for a peace deal between the rival factions and threatened to further disrupt Libya's oil industry.
Two eastern operations of state oil firm NOC - which have in the past made broad statements backing Haftar - on Sunday for the first time specifically said they supported his offensive. The NOC as a whole has tried to stay out of the conflict.
A Reuters team visiting the southern suburb of Ain Zara on Sunday estimated the Tripoli forces had gained up to 1,500 metres compared to a visit a few days earlier.
Other parts of the frontline appeared unchanged and the situation remains fluid. Both sides have gained and lost territory within days or even hours during the fighting.
"We are progressing. We are now in the phase of expelling the enemy from the capital," Salah Badi, a commander from the western city of Misrata allied to Tripoli, told Reuters.
The North African country has been in a state of chaos since Muammar Gaddafi was toppled in 2011 with Western intervention. The latest flare-up threatens to leave a power vacuum that Islamist militants could exploit.
The Libyan National Army have said the Tripoli govenrment is controlled by terrorist militias and that they are fighting to expel the militants.
Supporters of the Tripoli government have accused him of making a power grab with the backing of foreign countries.
Two NOC units based in areas under Haftar's control issued statements supporting the offensive on Sunday, a day after their Tripoli headquarters had condemned all military use of its facilities.
Benghazi-based AGOCO congratulated Haftar's LNA "on the success and progress in its striving against extremist terrorist militias and militias which steal public funds".
A separate NOC unit in the east, Sirte Oil Co, also issued a statement backing the Tripoli advance.
The Libyan National Army said on Saturday they had sent a warship to the eastern Ras Lanuf oil port for "training purposes".
A port engineer said the ship's arrival had not affected oil exports, which were as normal.
*This story was edited by Ahram Online