Syrian opposition groups say the army has been shelling the Damascus suburbs of Irbin and Harasta amid reports of several military offensives.
Opposition activists said the army turned tank, artillery and anti-aircraft guns on the two Damascus suburbs, which were retaken from rebels two months ago but have seen renewed insurgency in recent days.
The suburbs are a linked series of towns inhabited mostly by members of Syria's Sunni Muslim majority, grown increasingly resentful at the domination of the Assads, who belong to the minority Alawite sect, an offshoot of Shi'ite Islam.
Meanwhile the United Nations Security Council, including Russia and China, has agreed to a statement on Syria that backs UN-Arab League envoy Kofi Annan's bid to end the violence.
The statement also threatens Syria with "further steps" if it fails to comply with Annan's six-point peace proposal, which calls for a cease-fire, political dialogue between the government and opposition, and full access for aid agencies.
Annan dispatched a team of five experts to Damascus 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.
"We do not know how events will unfold. But we do know that we all have a responsibility to work for a resolution of this profound and extremely dangerous crisis," Ban said in a speech in the Indonesian capital Jakarta.
Watch our exclusive report on the horror unfolding in the city of Homs
Syria lies in a pivotal position at the heart of a web of regional conflicts in the Middle East, comprising a mix of faiths, sects and ethnic groups, and diplomats fear the 12-month uprising is degenerating into a full-blown civil war.
Forces loyal to President Bashar al-Assad have made gains against rebels around the country in recent weeks, but the violence shows no sign of abating, with reports of several army offensives.
Elsewhere the army fired 11 mortar rounds into the Khalidiya district of Homs, the day after 14 people died in the same area from mortar attacks, the British-based Syrian Observatory for Human Rights said.
Artillery shells targeted the rebel town of Rastan, north of Homs city, in the centre of Syria, and Qalat Mudiq, north west of Hama city, where an armoured personnel carrier came under fire. One soldier was killed in the attack, activists said.
Video footage showed shelling of the ancient Apamea castle at Qalat Mudiq. Reports from Syria cannot be independently verified because the authorities have barred access to rights groups and journalists.
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"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 on Tuesday.
"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 tone 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 mainly non-violent demonstrations last March, but the situation deteriorated rapidly in the face of a ferocious army crackdown.
Russia has previously vetoed two western and Arab-backed UN resolutions condemning government violence, arguing that the actions of rebels should also be criticised.
25 April 2011