The United Nations says Sri Lanka's Tamil Tiger rebels are preventing U.N. staff and their families from leaving rebel-controlled areas in the country's north.
U.S.-based Human Rights Watch has also accused the rebels of preventing civilians from fleeing the fighting, and of forcing some to fight against the government.
The country's army has barred aid workers from the war zone, raising further concerns about the safety of civilians.
Rebels have been fighting for an independent homeland for ethnic Tamils since 1983. More than 70-thousand people have died in the conflict.