Moscow, Jun 13 (IANS/RIA Novosti): UN observers in Syria are worried that violence is escalating around the Syrian opposition stronghold city of Homs, the UN said.

"UN observers reported heavy fighting in Rastan and Talbiseh, north of the city, with artillery and mortar shelling, as well as firing from helicopters, machine guns and smaller arms," said UN Supervision Mission in Syria (UNSMIS) spokeswoman Sausan Ghosheh.

"In Talbiseh, UN observers reported that the Free Syrian Army have captured Syrian Army soldiers," Ghosheh said in a statement.

Heavy artillery shelling and machine gun firing were audible in downtown Homs.

According to UN estimates, over 10,000 people, mostly civilians, have been killed in Syria and thousands displaced since the uprising against President Bashar al-Assad began about 15 months ago.

Ghosheh said the UNSMIS has called on all sides to stop violence and ensure that civilians are protected and international law respected.

She said the mission urges all parties to provide UNSMIS observers with immediate unrestricted access to conflict zones.

The statement came after two massacres in Syria's Houla and Hama in May and early June that killed dozens, including women and children.

UN and Arab League special envoy Kofi Annan has also expressed concern over the recent reports of violence escalation by both government and opposition forces.

US State Department officials met Russian foreign ministry officials in Moscow last week to try to hammer out a common position on the escalating crisis in Syria.