UN human rights chief Michelle Bachelet has warned that attacks on civilians in Libya could amount to war crimes.
She urged all sides to avoid bloodshed as military strongman Khalifa Haftar's forces advance on the UN-recognised government in Tripoli.
Some 47 people have been killed over the past three days, says the World Health Organization (WHO), as his forces seek to capture the capital.
The UN's special envoy to Libya, Ghassan Salame, hinted that a peace conference due to start this Sunday could be postponed, saying it would be convened "as soon as possible".
Libya has been torn by violence, political instability and power struggles since long-time ruler Muammar Gaddafi was deposed and killed in 2011.
What has Ms Bachelet said?
The rights commissioner said that the people of Libya "have long been caught between numerous warring parties, with some of the most vulnerable suffering some of the gravest violations of their human rights".
She said: "The attack near Mitiga airport [on Monday] that left many civilians in Tripoli stranded brought into stark focus the imperative for all parties to respect international humanitarian law, and to take all possible measures to protect civilians and civilian infrastructure, including schools, hospitals and prisons."
What are the latest casualties?
As well as the 47 deaths, 181 people were said to have been injured in recent clashes, the WHO said.
That was a higher toll than numbers given by either side, and appeared to be mainly fighters, it said.
Nine of the dead were civilians, including two doctors who it said had been "providing critically needed services to civilians in Tripoli. One doctor was reportedly killed while working as part of a field ambulance service".
The WHO said it had documented more than 40 attacks on health services in Libya over the course of 2018 and 2019. Targeted attacks on health services were a violation of international law, the organisation said.
At least 2,800 people have so far fled fighting around Tripoli, the UN says.
It also warns that those who remain risk being cut off from vital services because of the clashes.
Much of the international community, including the US, has called for a ceasefire.
The US military is among those to withdraw its supporting forces based in the country, blaming the "complex and unpredictable" situation and "increased unrest" on the ground.
The UN is also due to pull out non-essential staff.
Who is fighting?
Gen Haftar, who leads the Libyan National Army (LNA) from a stronghold in the east, declared an offensive to take control of Tripoli from Libya's UN-backed government last week.
Prime Minister Fayez al-Serraj, the head of the Government of National Accord (GNA), has accused him of attempting to carry out a coup.
The GNA was created from peace talks in 2015 but has struggled to take control of the country.
Gen Haftar helped Gaddafi seize power in 1969 before falling out with him and going into exile in the US.
He then returned when the uprising against Gaddafi began and became a rebel commander.
His LNA troops have continued to make advances, seizing the south of Libya and its oil fields earlier this year.
UN-backed talks between the rival governments had been scheduled for 14-16 April to discuss a roadmap for new elections, but it is now unclear if these will still take place.
Mr Serraj said he had offered concessions to Gen Haftar to avoid bloodshed, only to be "stabbed in the back".