The death toll from the attack has risen to at least 53. A UN humanitarian report said there were two air strikes, not one as reported earlier, and that guards shot at migrants who were trying to run for their lives.
The United Nations said on Thursday it had information that Libyan guards shot at refugees and migrants trying to flee from air strikes that hit a migrant detention centre late on Tuesday, killing least 53 people.
A UN humanitarian report said there were two air strikes, one hitting an unoccupied garage and one hitting a hangar containing around 120 refugees and migrants.
"There are reports that following the first impact, some refugees and migrants were fired upon by guards as they tried to escape," the UN report said.
The UN had initially put the death toll at 44 and the wounded to more than 130 while it was thought to be one attack. The wounded include six children.
A divided UN Security Council on Wednesday failed to condemn the attack on the detention centre which held mostly African migrants.
During a two-hour closed-door meeting, Britain circulated a statement that would have condemned the deadly air strike blamed on warlord Khalifa Haftar's militia, called for a ceasefire and a return to political talks.
But US diplomats told the meeting that they required a green light from Washington to approve the text and the talks ended without US approval, sources told AFP.
TRT World's Philip Owira reports.
Peru's Ambassador Gustavo Meza-Cuadro, whose country holds the council presidency, told reporters that discussions were continuing on the press statement but council diplomats said they did not expect a response.
Haftar, who holds sway in eastern Libya, launched an offensive in April to seize Tripoli, seat of a UN-recognised government that is backed by various militias.
World powers have been divided on how to respond to Haftar's military campaign, with the United States and Russia refusing to back UN calls for a ceasefire.
The proposed statement would have called on warring sides to "immediately de-escalate the situation and commit to a ceasefire".
The government of national accord, based in Tripoli, said Haftar's militia was responsible for the strike on the detention centre.
A US State Department statement released in Washington earlier condemned the "abhorrent" air strike but did not call for a ceasefire.
UN Secretary-General Antonio Guterres earlier said he was outraged and called for an independent investigation into the deadly strike.
He said that the United Nations had shared the coordinates of the detention centre with the warring sides to ensure that civilians sheltering there were safe.