The United Nations on Tuesday postponed a Libyan national conference aimed at drawing up an election roadmap because of fighting raging near the capital, in another setback to peace efforts.
"We cannot ask people to take part in the conference during gunfire and air strikes," UN envoy Ghassan Salame said.
He expressed hope that the meeting, which had been scheduled for next week, would take place "as soon as possible".
The UN Security Council is to hold closed-door consultations on Wednesday on the crisis in Libya and hear a briefing from Salame, diplomats in New York said.
UN chief Antonio Guterres called for an "immediate halt" to hostilities, after Tripoli s only functioning airport was hit in an air strike on Monday by strongman Khalifa Haftar s self-styled Libyan National Army (LNA).
After a night-time lull, fighting resumed on Tuesday morning south of the city, a security source said.
The suburb of Wadi Rabi was under the Government of National Accord s (GNA s) control, its spokesman Colonel Mohamed Gnounou said on Tuesday, adding that Haftar s forces had been pushed back towards the regions of Soug Al-Khamis and Al-Aziziya to the south.
Gnounou said the Tripoli based unity government had carried out several air raids against LNA positions south of Tripoli, and also hit supply lines in central Libya.
The UN s high commissioner for refugees, Filippo Grandi, called on Tuesday for the warring parties to "spare civilians, including refugees and migrants trapped in the country".
The UN s refugee agency said it had evacuated more than 150 refugees from a Tripoli detention centre, and that migrants elsewhere might also need to be moved.
Led by Fayez al-Sarraj, the GNA s authority is not recognised by a parallel administration in the east of the country, which is allied with Haftar.
LNA spokesman Ahmad al-Mismari accused the unity government of "allying itself with Islamist militias".
"The battle is no longer in the hands of al-Sarraj -- it is henceforth in the hands of terrorists", Mesmari said, citing pro-GNA militias coming from the city of Misrata 200 kilometres (120 miles) east of the capital.
Haftar's forces, which launched a surprise offensive on the Libyan capital last week, claimed responsibility for Monday s air raid on Mitiga airport.
It caused no casualties, but left a metre-deep (yard-deep) crater on a runway.
Salame said the air strike constituted "a serious violation of international humanitarian law which prohibits attacks against civilian infrastructure".
Flights were suspended on Monday, but the airport was due to be reopened to night-time flights late on Tuesday.
Hafter has defied international calls to halt the advance, including from the UN Security Council and the United States.
The GNA s health ministry on Monday put the death toll in the fighting at 35. Haftar s forces have said 14 of their fighters have died.
The UN said the clashes have displaced some 3,400 people.
French President Emmanuel Macron spoke with Sarraj to voice his "total opposition to the offensive against the capital and the endangering of civilian lives", the unity government said.
The French presidency said in a statement that Macron had also been in contact with Haftar and said it was "imperative" that the fighting ends immediately.
International efforts to end the Libyan conflict have repeatedly failed.
Rival leaders agreed last year to hold elections before December 10, 2018 under a French plan, but that vote never materialised.
The national conference, which had been scheduled for April 14-16 in the central city of Ghadames, aimed to fix dates for legislative and presidential elections, and work towards a new constitution.
UN High Commissioner for Human Rights, Michelle Bachelet, urged all parties to remember "their obligations under international law to ensure the protection of civilians and civilian infrastructure".
Russia has said meanwhile it is not taking sides in the fighting in Libya but behind the scenes, experts say, Moscow is firmly backing Haftar.
"He is supplied with Russian weapons and gladly takes them. He is Moscow s man," said analyst Alexander Shumilin of the Centre for the Analysis of Middle East Conflicts in Moscow.
On the other side of the fight, Sarraj s UN-backed government retains substantial support from former colonial power Italy.