BEIRUT — The head of the United Nations observer mission in Syria on Sunday urged both sides in the conflict to take “immediate action” to facilitate the evacuation of civilians trapped amid escalating violence.

“The parties must reconsider their position and allow women, children, the elderly and the injured to leave conflict zones, without any preconditions, and ensure their safety,” Gen. Robert Mood said in a statement.

The Norwegian general spoke a day after the U.N., citing a recent increase in hostilities, suspended its observer mission in Syria, raising new questions about the fate of a faltering U.N.-brokered peace plan.

The almost 300 unarmed observers will remain in Syria but will refrain from going out on patrols “until further notice,” the U.N. said. The observers have had several close calls, but the U.N. has reported no serious injuries among its staff.

Among other objectives, the peace plan written by U.N. special envoy Kofi Annan called for a cease-fire in Syria and a daily, two-hour humanitarian “pause” in the fighting, designed to allow time to evacuate civilians and the wounded. But prospects for the cease-fire appear to have dimmed in recent days as the fighting has intensified.

A British-based opposition group, the Syrian Observatory for Human Rights, said that more than 1,000 families were stranded in the central city of Homs, the epicenter of the revolt against the government of President Bashar Assad. Government forces have been shelling rebel-held districts in Homs, the suburbs of Damascus and elsewhere, the opposition says.

According to the anti-Assad activists, scores of people have been killed in military bombardments and other government attacks, as government security forces have sought to oust rebels from strongholds across the country. There was no independent confirmation of the extent of casualties.

Attempts to extricate civilians from Homs during the last week have been unsuccessful, Gen. Mood said.

The observer chief is expected to brief the U.N. Security Council on Monday about the deteriorating situation in Syria, where a 15-month uprising has resulted in at least 10,000 deaths. Tens of thousands of Syrians have already fled their homes because of the fighting, human rights groups say.

Opposition activists repeatedly called on the U.N. to take more robust action against the Syrian government, possibly including economic sanctions and an arms embargo. But Russia, a longtime ally of Assad, has blocked any U.N. move to penalize Syria. The Syrian government says it is fighting “terrorists” and a “foreign conspiracy.”

The U.N. must also decide the fate of the observer mission; its mandate expires July 20. The world organization could extend the mission, end it, or take some other action with regard to Syria.

patrick.mcdonnell@latimes.com