Syria rebels quit eastern city, army on offensive, tanks enter residential neighborhoods

Syrian army soldiers raid a building as they search for Syrian rebels in a suburb of Damascus, Syria, on Tuesday, March 20, 2012. An international human rights group accused Syria's armed opposition on Tuesday of carrying out serious abuses, including the kidnapping and torture of security forces, in a sign of the growing complexity of the year-old uprising against President Bashar Assad. (AP Photo)

BEIRUT (Reuters) - Rebel fighters were forced to flee the eastern Syrian city of Deir al-Zor on Tuesday in the face of a fierce army assault, suffering the latest setback in their bid to oust President Bashar al-Assad.

In a separate blow to their cause, a respected human rights group accused the armed opposition of committing torture and arbitrary executions during the 12-month uprising - charges previously only leveled at the state security apparatus.

Despite recent successes, Assad still faces significant outside pressure. Ally Russia signaled on Tuesday it would support a U.N. statement backing a mission by envoy Kofi Annan to end the bloodshed so long as there was no ultimatums.

In addition, Moscow joined calls for both the army and rebels to grant daily ceasefires that would enable humanitarian missions to areas of Syria worst hit by the fighting.

The lightly armed rebel forces have been forced into retreat across the country in recent weeks, with the army using heavy armor to chase them from towns and cities, chalking up its latest victory in Deir al-Zor, which lies on the road to Iraq.

"Tanks entered residential neighborhoods, especially in southeastern areas of Deir al-Zor. The Free Syrian Army pulled out to avoid a civilian massacre," a statement by the Deir al-Zor Revolution Committees Union said.

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