Heavy fighting has erupted south of Tripoli after Libya's UN-backed government announced a counter-offensive against insurgent forces.
It comes after days of little advances by either side, in clashes which have killed 220 people. Soldiers loyal to Gen Khalifa Haftar launched an attack earlier this month, intending to take Tripoli.
Prime Minister Fayez al-Serra has condemned the "silence" of his international allies amid the fighting.
Details of progress by both sides were not immediately apparent.
Mr. Serra's Government of National Accord says it has carried out seven airstrikes on areas held by Gen Haftar's Libyan National Army (LNA).
The group has been advancing on the city from multiple directions and says it has taken Tripoli's international airport.
The UN-backed government says it has launched a counter-offensive against Gen Haftar's forces.
Gen Haftar, a former army officer, was appointed chief of the LNA in 2015 under an earlier, internationally recognized government based in Tobruk. He has support from Egypt, Russia, and the UAE.
The White House says President Trump has spoken to Gen Haftar, suggesting the US may also endorse a new government under his command.
Both America and Russia have refused to support a UK-drafted UN Security Council resolution calling for a ceasefire.
An LNA spokesperson told AFP news agency: "We have won the political battle, and we have convinced the world that the armed forces are fighting terrorism."
Gen Haftar has support from several foreign powers, who see him as a potentially stabilizing force in the chaos of post-revolution Libya, BBC Arab Affairs editor Sebastian Usher reports.
Some Libyans feel the same way, but others see him as just another warlord bent on winning power by force, our editor.
Libya has been torn by violence, and political instability since long-time ruler Muammar Gaddafi was deposed and killed in 2011.