Images show migrants boarding a bus after being detained by the local security forces following an escape attempt from the facility.

Details of what triggered the incident are unknown according the International Organization for Migration (IOM), adding that at least 20 other migrants were wounded and that many more had escaped in the chaos.

The killings came a week after sweeping raids in Tripoli, mostly targeting irregular migrants, left at least one person dead and 15 wounded, according to the UN Support Mission in Libya (UNSMIL).

Doctors without Borders (MSF) said 5,000 migrants and refugees had been swept up in “violent mass arrests”, tripling the numbers detained in the city in just five days.

Libyan authorities had said the wave of detentions last Friday and Saturday were part of anti-drug raids on houses and makeshift shelters in Gargaresh, a poor suburb of Tripoli.