Libyan officials say Khalifa Haftar's self-styled Libyan National Army has intensified its airstrikes over the past two days on rival militias in and around the capital, Tripoli.
The officials say Monday that airstrikes have targeted the Nawasi Brigade, one of several militias allied with a weak U.N.-supported government, in the Abu Salim district, about 7 kilometers (4 miles) from Tripoli's center.
They say airstrikes and shelling also hit the towns of Khallet al-Forjan, Ain Zara and al-Twaisha, south of Tripoli.
The officials requested anonymity because they weren't authorized to brief media.
Haftar, whose forces control much of eastern Libya, launched an offensive to retake the capital on April 4. The UN says the fighting has killed more than 270 people, including civilians, and displaced more than 41,000.
Forces backing Libya's internationally recognised government fought house-to-house battles with troops loyal to commander Khalifa Haftar in southern parts of the capital Tripoli on Sunday and appeared to be gaining ground.
Government soldiers, some in jeans and t-shirts, took cover by abandoned buildings as they fired on Haftar's positions. Some carried anti-aircraft guns they had to remove from their trucks to get through the narrow streets.
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Haftar's Libyan National Army (LNA), which is allied to a rival administration in eastern Libya, mounted an offensive on Tripoli three weeks ago but has failed to breach defenses in the city's south despite heavy fighting.
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 neighbourhood 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 fighting the LNA, told Reuters.