BEIRUT (AP) — The U.N. High Commissioner for Human Rights says she is concerned about the condition of some 200 families trapped in the last remaining area held by the Islamic State group in eastern Syria.

Michelle Bachelet says in a statement Tuesday that the extremists are actively preventing civilians, including women and children, from leaving the tiny area near the border with Iraq, which is currently besieged by U.S.-backed Syrian fighters.

Some 300 militants are mixed in with hundreds of civilians and are refusing to surrender while trying to negotiate an exit with the U.S.-backed forces surrounding them.

The Syrian Observatory for Human Rights, a Britain-based war monitor, said some 50 trucks entered the IS-held area, apparently to bring out some of the people trapped inside.