Two large suburbs of Damascus came under heavy tank bombardment on Wednesday following renewed Free Syrian Army attacks on forces loyal to President Bashar al-Assad, opposition activists said.
Artillery and anti-aircraft gun barrages hit the suburbs of Harasta and Irbin, retaken from rebels by Assad's forces two months ago, and army helicopters were heard flying over the area, on the eastern edge of the capital, the activists said.
Assad's forces reasserted their control of Damascus suburbs in January after days of tank and artillery shelling that beat back rebels and lessened street protests against the 42-year rule of Assad and his father, the late President Hafez al-Assad.
The suburbs are a linked series of towns inhabited mostly by members of Syria's Sunni Muslim majority, who have grown increasingly resentful at the domination of the Assads, who belong to the minority Alawite sect, an offshoot of Islam.
The Damascus assault and rebel fighters' flight on Tuesday from the eastern city of Deir al-Zor mark the latest setbacks for the armed opposition, which also faced accusations of torture and brutality from a leading human rights body.
But as Assad made advances on the ground, he appeared to suffer a setback on the diplomatic front, with key-ally Moscow adopting a new, sharper tone after months of publicly standing by his government.
We believe the Syrian leadership reacted wrongly to the first appearance of peaceful protests and ... is making very many mistakes, Foreign Minister Sergei Lavrov told Russian radio station Kommersant-FM.
This, unfortunately, has in many ways led the conflict to reach such a severe stage.
Lavrov also spoke of a future transition period for Syria but continued to reject calls from most Western and Arab states for Assad to resign, saying this was unrealistic.
It was not immediately clear if the change in language would translate into a tangible difference in the way international powers, hitherto divided on Syria, might deal with the crisis.
The change in the Russian position is one of tone, not of substance. Moscow still sees its support of Assad as part of a regional game, but it is losing the support of the Syrian people, which could backfire on it if the Syrian regime falls, said Najati Tayyara, a prominent Syrian opposition figure.
The uprising started with non-violent demonstrations last March, but the situation deteriorated rapidly amid a ferocious army crackdown and there are now daily clashes between rebels and security forces around the country.
The United Nations says more than 8,000 people have been killed so far, but the toll is rising rapidly, with at least 31 men, women and children killed on Tuesday, the British-based Syrian Observatory for Human Rights reported.
CIVIL WAR FEARS
Lightly armed rebel forces have been forced into retreat across the country in recent weeks, with the army using heavy weapons to chase them from towns and cities, chalking up its latest victory in Deir al-Zor.
Tanks entered residential neighbourhoods, especially in south-eastern 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.
After failing to hold significant stretches of land, analysts say the rebels appear to be switching to insurgency tactics, pointing to bloody car bomb attacks in two major Syrian cities at the weekend and the sabotage of a major rail link.
Car bomb attacks in the capital Damascus and second city Aleppo killed at least 30 over the weekend, while rebels also destroyed a railway bridge linking Damascus to Deraa, according to official Syrian media.
Diplomats warn the fighting could develop into a civil war pitching Assad's Alawite sect and its minority allies against the majority Sunni Muslim population.
Assad may also be facing pressure from inside his government. Documents described as leaked from inside Syria's embattled government show it trying to dissuade the president's allies from defecting.
The government says 2,000 members of the security forces have been killed by foreign-backed terrorists and denies accusations of brutality and indiscriminate violence.
In a new twist, the advocacy group Human Rights Watch said the rebels were guilty of serious crimes, citing cases of kidnapping, torture and killings in cold blood.
Washington said it would absolutely denounce human rights violations by the rebels, but stressed that most of the abuse was being carried out by pro-Assad forces.
Russia has previously vetoed two Western and Arab-backed U.N resolutions condemning government violence, arguing that the actions of rebels should also be criticised.
In a fresh effort to form a united international front, France has circulated a Western-drafted statement for the sharply divided U.N. Security Council deploring the turmoil and backing peace efforts by U.N.-Arab League envoy Kofi Annan.
Russia announced it would back the text on two conditions - that there was no ultimatum imposed on Assad and that Annan release full details of his peace plan.
Annan dispatched a team of five experts to Damscus on Monday to discuss ways of implementing the peace drive, including a mechanism to let international monitors into the country. Syria has questioned the value of such a mission and talks continue.
Lavrov also dismissed media reports of Russian warships entering Russia's naval facility in the Syrian port of Tartous as fairy tales. Some reports had said Russian ships were delivering weapons or special forces troops.
Lavrov said a Russian tanker with fuel for Russian warships involved in anti-piracy operations in the Gulf of Aden was docked at the port. Russia has repeatedly said its arms sales to Syria violate no laws and it sees no grounds to suspend them.
(Additional reporting by Oliver Holmes and Crispian Balmer in Beirut, Steve Gutterman in Moscow and Matt Spetalnick in Washington; Writing by Crispian Balmer; Editing by Louise Ireland)