In a joint report, the UN Support Mission in Libya (UNSMIL) and the UN human rights office in Geneva called for those responsible to be held to account.

They urged Libyan authorities to "conduct independent, impartial and thorough investigations... with a view to ensuring swift prosecution" of those behind the July 2 raids that left 53 people dead and 130 wounded.

"As I have said previously, the Tajoura (suburb) attack, depending on the precise circumstances, may amount to a war crime," said Michelle Bachelet, the UN High Commissioner for Human Rights.

A hangar used to detain migrants took a direct hit in the night-time strikes along with a workshop operated by an armed group.

It was one of the deadliest incidents since the forces of eastern military strongman Khalifa Haftar launched an offensive in April against the Tripoli-based Government of National Accord.

The UN report did not name the party responsible for the strikes, which the GNA has blamed on Haftar's fighters, despite the latter's denials.

But the report said it was likely carried out by a foreign backer of Haftar.

"While it appears the airstrikes... were conducted by aircraft belonging to a foreign State, it remains unclear whether these air assets were under the command" of Haftar "or operated under the command of that foreign State in support" of the general, it said.