In a barrage of shelling, Syrian forces killed 200 people and wounded hundreds early Saturday in Homs in an offensive that appears to be the bloodiest episode in the nearly 11-month-old uprising, activists said.
The offensive was reported in Homs, which has been one of the main flashpoints of opposition to the regime during the uprising against President Bashar Assad.
Two main opposition groups, the British-based Syrian Observatory for Human Rights and the Local Coordination Committees, said the death toll was more than 200 people. More than half of the killings — about 140 — were reported in the Khaldiyeh neighborhood.
"This is the worst attack of the uprising, since the uprising began in March until now," said Rami Abdul-Rahman, the head of the Observatory, which tracks violence through contacts on the ground.
The reports could not be independently confirmed.
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.
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 U.N. Security Council meeting later Saturday was to take up a much-negotiated resolution on Syria. A diplomat for a Western nation that sits on the council said the meeting would happen Saturday morning. The diplomat spoke Friday on condition of anonymity because he was not authorized to be quoted by the press.
The move toward a vote came after 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 U.S. 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.
Clinton called Lavrov while flying Friday to Munich for a security conference that both are attending, State Department spokesman Mark Toner said.
He said Clinton and Lavrov agreed to have American and Russian diplomats continue work on a Syria resolution and were planning to meet for more talks in the German city over the weekend.
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 U.N. 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.