The U.N. human rights chief says thousands of lives are at risk in parts of conflict-ridden Libya, decrying an escalation of attacks in residential areas with artillery, rockets and airstrikes.

Michelle Bachelet's office highlighted her "grave concern" about thousands of civilian men, women and children stuck in conflict-hit areas of Tripoli, the capital, in a statement Tuesday.

She also expressed concerns about some 3,350 migrants and refugees held in detention centers near the conflict zones. She pointed to reports of food and water shortages that some face.

The statement said some "are reportedly being forced to work for militias controlling their detention centers."

Bachelet called for efforts to allow trapped civilians to leave conflict areas, and urged an immediate ceasefire and a resumption of political talks.