In a barrage of mortar shells, Syrian forces killed at least 337 people and wounded 1,300 in Homs in an offensive that appears to be the bloodiest episode in the nearly 11-month-old uprising, the Al Arabiya news nework and Syrian opposition officials said Saturday.

Al Arabiya cited eye witnesses as saying that the bombardment, which began late Friday, continued on Saturday morning. Security forces continued to pour into the city due to fears that civilians might attempt to retaliate. A field hospital in the Khaldiyeh neighborhood was destroyed in the shelling.

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The assault in Homs, which has been one of the main flashpoints of opposition during the uprising, comes as the UN Security Council prepares to vote on a draft resolution backing an Arab call for President Bashar Assad to give up power.

"This is the worst attack of the uprising, since the uprising began in March until now," said Rami Abdul-Rahman, the head the Syrian Observatory for Human Rights, which tracks violence through contacts on the ground.

Homs on Friday night

Earlier Saturday, the Syrian government denied launching the deadly offensive, saying that civilians who were killed overnight died at the hand of "gunmen," the official SANA news agency reported.

According to the report, news footage broadcast by satellite channels showed "civilians who were kidnapped and killed by gunmen."

The regime accused militants of trying to pressure the UN to pass an anti-Assad resolution.

It was not immediately clear what precipitated the attack, but there have been reports that army defectors set up checkpoints in the area and were trying to consolidate control.

UN to vote on resolution

Earlier on Friday, deadly clashes erupted between government troops and rebels in suburbs of the Syrian capital and villages in the south, sparking fighting that killed at least 23 people, including nine soldiers, activists said.

Assad is trying to crush the revolt with a sweeping crackdown that has so far claimed thousands of lives, but neither the government nor the protesters are backing down and clashes between the military and an increasingly bold and armed opposition has meant many parts of the country have seen relentless violence.

The UN Security Council will meet Saturday morning to take up a much-negotiated resolution on Syria, said a diplomat for a Western nation that sits on the council.

The diplomat spoke Friday on condition of anonymity because he was not authorized to be quoted by the media.

The move toward a vote came after US Secretary of State Hillary Rodham Clinton spoke by telephone with Russian Foreign Minister Sergey Lavrov in an effort to overcome Russian opposition to any statement that explicitly calls for regime change or a military intervention in Syria.

The US and its partners have ruled out military action but want the global body to endorse an Arab League plan that calls on Assad to hand power over to Syria's vice president.

Russia's deputy foreign minister, Gennady Gatilov, said Friday that Moscow could not support the resolution in its current form. But he expressed optimism that an agreement could be reached, according to state news agency RIA Novosti.

Assad's regime has been intensifying an assault against army defectors and protesters. The UN said weeks ago that more than 5,400 people have been killed in violence since March. Hundreds more have been killed since that tally was announced.

Roi Kais, AP and AFP contributed to the report

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