An attack which killed more than 44 migrants at a detention centre outside the Libyan capital could constitute a war crime, a UN official said.
At least 130 people were injured in the attack, which the Libyan government blamed on an air strike by forces loyal to a warlord, General Khalifa Haftar.
Gen Haftar’s forces accuse the government side of shelling the centre.
Most of the dead are believed to be sub-Saharan Africans who were attempting to reach Europe from Libya.
Thousands of migrants are being held in government-run detention centres in Libya. The location of the centre attacked on Tuesday and the information that it housed civilians had been passed to all parties in Libya’s conflict, the UN’s High Commissioner for Human Rights, Michelle Bachelet, said.
“This attack may, depending on the precise circumstances, amount to a war crime,” she said. It was the second time the shelter was hit, she added.
Separately, the UN Security Council has changed its agenda, and will discuss the situation in Libya behind closed doors later today.
Libya has been torn by violence and division since long-time ruler Muammar Gaddafi was deposed and killed in 2011.
A hangar housing migrants at the Tajoura Detention Centre, which houses 600 migrants, reportedly took a direct hit.
Women and children were among the victims, 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 issued a stark warning in May that those living in the Tajoura centre should be moved immediately out of harm’s way. “The risks are simply unacceptable at this point,” the UN refugee agency said.
According to Sebastian Usher, Arab affairs editor, the UN and aid agencies have been warning that a tragedy like this has been all but inevitable as the renewed fighting in and around Tripoli has put migrants held in detention camps directly in the line of fire.
The plight of migrants was already desperate, prey to human traffickers and militias.
The UN has said that the airstrike on Tajoura shows that the EU policy of sending people trying to cross the Mediterranean to Europe back to Libya must be ended.
It’s been successful in radically cutting the numbers of those getting into Europe by that route – although others have since opened up. But humanitarian agencies say the human cost is too high.
With General Khalifa Haftar’s assault on Tripoli stalled, the chances are that his forces may resort to indiscriminate attacks that could endanger civilian lives further.
But the militias who hold the migrants in such appalling conditions, so close to what is now a frontline, must also take a share of the blame for what has happened.