Air strikes hit Tripoli’s only functioning airport on Monday and flights were cancelled as the most serious escalation in violence in Libya for years rumbled on.
Six passenger flights were cancelled and passengers moved to safety from Metiga Airport in eastern Tripoli as two rockets were fired by a fighter jet from the east Libyan forces.
At least 25 people were killed and 50 people wounded in clashes, the internationally recognised Government of National Accord in Tripoli said.
The UN said more than 2,800 people had fled fighting that increased “the misery of refugees and migrants arbitrarily detained in detention centres in areas of active conflict”.
Brigades loyal to the GNA said they had wrested back control of the disused international airport in southern Tripoli from the forces of eastern commander Field Marshal Khalifa Haftar.
His Libyan National Army launched an operation to take the capital last week and said 22 of its fighters had been killed.
The former international airport was destroyed during inter-factional fighting in 2014 and was being rebuilt.
GNA military spokesman Col Mohamed Gnounou said on Sunday Operation Volcano of Anger had been launched to "purge all Libyan cities of aggressor and illegitimate forces", referring to Field Marshal Haftar's fighters.
On Monday, EU foreign ministers gathered in Luxembourg to urge an end to hostilities but without proposing concrete steps.
British Foreign Minister Jeremy Hunt tweeted: “The UK is engaging all partners to send an unambiguous message on Libya.
"Consensus from European foreign ministers this morning: no military solution. The UN process must be supported.”
Mr Hunt said on Sunday night there was “no justification for the LNA move on Tripoli”.
EU foreign policy chief Federica Mogherini said earlier that the united European message should be for “a full implementation of the humanitarian truce and to avoid any further military action and escalation, and a return to the political track”.
The LNA initially faced little resistance when entering the town of Gharyan, 80 kilometres to the south of the capital, last week but has struggled to advance further than the southern suburbs of Tripoli and the town of Zawiya to the west.
The GNA is largely protected by militias in the capital but has been reinforced by brigades from nearby battle-hardened cities in recent days.
The LNA says it wants to rid Tripoli of the armed groups, which it sometimes refers to as terrorists.
Field Marshal Haftar has steadily extended his control over eastern and southern Libya in recent years but the fighters in the north of the country provide a harder foe.
The LNA offensive has been widely condemned by the international community, with the UN failing to secure a two-hour humanitarian ceasefire on Sunday as both sides unleashed their war planes and heavy weapons.
"We have made it clear that we oppose the military offensive by Haftar's forces and urge an immediate halt to these military operations against the Libyan capital," US Secretary of State Mike Pompeo said on Sunday.
"This unilateral military campaign against Tripoli is endangering civilians and undermining prospects for a better future for all Libyans."
Mr Pompeo stressed that there was "no military solution to the Libya conflict", and urged all parties to return to political negotiations mediated by the UN.
The US military also announced on Sunday that it had temporarily pulled troops out of Libya "in response to security conditions". It was the first admission that American soldiers were there.
Libya has been riven by chaos since the Nato-backed uprising in 2011 that killed dictator Muammar Qaddafi, as rival administrations and armed groups battle for power.
On Friday, the UN Security Council called on Field Marshal Haftar's force to halt its advance and warned that the offensive would further destabilise the country.
But on Sunday, Russia – a supporter of Field Marshal Haftar – blocked proposals for the council to adopt a formal statement, diplomats said, and instead insisted that all Libyan forces should be urged to stop fighting.
UN Secretary General Antonio Guterres was visiting Libya ahead of a planned UN-backed national conference aimed at uniting Libyan rivals and paving the way for elections.
Ghassan Salame, who leads the UN Support Mission for Libya, insisted the conference in the south-western town of Ghadames would go ahead between April 14 and 16.