Syria forces 'in Homs massacre'
Activists accused the military of carrying out a massacre after a night of shelling in the city. Unverified videos on the web showed many bodies.
But the government denied the claims, saying activists were engaging in a propaganda campaign.
The UN Security Council is due to vote later on a resolution that is likely to call for a transfer of power in Syria.
Russia has said it will veto any resolution calling on President Bashar al-Assad to stand down.
'Hysterical incitement'
An activist in Homs told the BBC that it was the worst violence he had seen since anti-government protests began last March.
"It's an awful situation. Two hours ago, three hours ago they started this shelling, we have no reason why," he said.
The UK-based Syrian Observatory for Human Rights and the Syrian Local Coordination Committees both said the death toll had exceeded 200 after mortar shelling began late on Friday.
The Syrian National Council, an umbrella group for Syria's opposition factions, said 260 people had died and accused government forces of "randomly bombing residential areas".
"The Syrian National Council calls on everyone around the world to speak up and do something to stop the bloodshed of innocent Syrians," it said in a statement.
The BBC's Jim Muir in Lebanon says a death toll higher than 200 would make it by quite a long way the bloodiest day since protests began.
But state media dismissed the reports as a "hysterical campaign of incitement" by armed gangs designed to influence the UN.
"The civilians shown by satellite television stations are citizens who were kidnapped and killed by armed gunmen," said a report on Sana news agency.
International media outlets are restricted in Syria, making it difficult to verify the claims of either side.
Meanwhile, activists have attacked Syrian embassies around the world.
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