Fighters loyal to the Government of National Unity are trying to defend their city from a two week long attack by the eastern based Libyan National Army.
Heavy clashes broke out in the southern districts of the Libyan capital Tripoli on Saturday as forces loyal to Libya's UN-recognised government launched a counterattack to fend off fighters allied to dissident General Khalifa Haftar.
Residents said they could hear shelling in the city centre as the death toll from two weeks of fighting between the country's rival governments rose to 220.
The rise in violence happened after the White House said on Friday that US President Donald Trump spoke by phone earlier in the week with Haftar, who started an offensive against Tripoli on April 3.
The disclosure of the call and a US statement that it "recognized Field Marshal Haftar's significant role in fighting terrorism and securing Libya's oil resources" has boosted the commander's supporters and enraged his opponents.
Western powers and the Gulf have been divided over a push by Haftar's forces to seize Tripoli, undermining calls by the United Nations for a ceasefire.
Despite the offensive, Haftar's Libya National Army (LNA) force has not been able to breach the southern defences of forces allied to the internationally recognised administration based in the city.
On Saturday, shelling was louder and more frequent than previous days and heard in central districts more than 10 km away from the frontline, residents said.
Both sides said there was progress in southern Tripoli, but no more details were immediately available.
A Reuters TV cameraman visiting the southern Khalat Furgan suburb heard heavy shelling but saw no apparent major change in the frontline.
On Friday, two children were killed in shelling in southern Tripoli, residents said. The fighting has killed 220 people an wounded 1,066, according to the World Health Organization (WHO).
On Thursday, both the United States and Russia said they could not support a UN Security Council resolution and called for a ceasefire in Libya.
Russia objects to the British-drafted resolution blaming Haftar for the latest flare-up in violence when Haftar's Liberal National Army advanced to the outskirts of Tripoli earlier this month, diplomats said.
The United States did not give a reason for its decision not to support the draft resolution, which would also call on countries with influence over the warring parties to ensure compliance and for unconditional humanitarian aid access in Libya.
The country has been gripped by conflict since Libya's former leader Muammar Gaddafi was toppled in 2011.