The fighting in Libya's capital has reached a detention center holding hundreds of detained migrants and refugees, the U.N. said Tuesday.

Stephane Dujarric, a spokesman for the U.N. secretary-general, said the U.N. aid agency has received reports that the Qasr Ben Ghashir detention center, holding some 890 refugees and migrants, was "breached by armed actors." The facility is 20 kilometers (12.5 miles) south of central Tripoli.

The U.N. says some 3,600 refugees and migrants are held in facilities near the front lines of fighting between the self-styled Libyan National Army and other heavily-armed militias. Five detention centers are in areas already engulfed by fighting, while six more are in close proximity to the clashes.

"The situation in these detention centres is increasingly desperate, with reports of guards abandoning their posts and leaving people trapped inside," Dujarric said, adding that one facility has been without drinking water for days.

Libya became a major conduit for African migrants and refugees fleeing to Europe after the uprising that toppled and killed Moammar Gadhafi in 2011. Thousands have been detained by armed groups and smugglers.

The latest fighting in Libya pits the LNA, led by Field Marshal Khalifa Hifter, against rival militias allied with a weak, U.N.-supported government. The World Health Organization says the fighting has killed more than 270 people, including civilians, and wounded nearly 1,300. It says more than 30,000 people have been displaced.