An air strike which killed more than 44 migrants at a detention centre on the outskirts of the Libyan capital Tripoli may amount to a war crime, the UN says.
More than 130 people were injured in the strike, blamed on forces led by warlord Gen Khalifa. His troops accuse the government of the attack.
Most of the dead are believed to be sub-Saharan Africans, attempting to reach Europe from Libya by sea.
Thousands of migrants are held in government-run detention centres.
The country has been torn by violence and division since long-time ruler Muammar Gaddafi was deposed and killed in 2011.
The head of the United Nations Mission in Libya, Ghassan Salama, expressed his shock at the attack inside a hangar at the Tajoura Detention Centre.
Tajoura houses some 600 migrants.
Women and children were among those hit, Guma El-Gamaty, a member of the UN-backed political dialogue group, told BBC World Service.
An official in the Libyan health ministry, Doctor Khalid Bin Attia, described the carnage for the BBC after attending the scene:
“People were everywhere, the camp was destroyed, people are crying here, there is psychological trauma, the lights cut off.
“We couldn’t see the area very clear but just when the ambulance came, it was horrible, blood is everywhere, somebody’s guts in pieces.”
The UN-backed Government of National Accord (GNA), led by Prime Minister Fayez al-Sarraj, accused the self-styled Libyan National Army (LNA) of carrying out an air strike on the centre.
The “heinous crime” was “premeditated” and “precise”, it said.
The LNA – led by Gen Haftar – was fighting government forces in the area where the strike happened.
It had announced on Monday that it would start heavy air strikes on targets in Tripoli after “traditional means” of war had been exhausted.
The LNA said its warplanes had bombed a pro-government camp near the centre and pro-government forces had fired shells in response, hitting the migrant centre by accident.
A spokesman for the UN refugee agency, Charlie Yaxley, said it could not confirm who was behind the attack on the centre, Reuters news agency reports.
“This bombing clearly amounts to the level of a war crime,” Mr Salama said in a statement.