Western nations stepped up demands for UN measures against President Bashar al-Assad after the Syrian leader ignored repeated calls for an end to the bloodshed in his country.
But UN Security Council battlelines were drawn when Russia's UN envoy said calls for sanctions did not help end the crackdown by Syrian security forces in which rights groups say more than 2,000 civilians have died.
UN Assistant Secretary-General Oscar Fernandez-Taranco briefed the 15-member Security Council behind closed doors about events in Syria in the week since the council called for an "immediate" halt to the violence.
Taranco was quoted as saying there had been no letup in the deaths of protesters -- with at least 87 people killed across the country on Tuesday alone -- while UN officials had met Syrian diplomats to try to get accurate information.
Syrian security forces cut power and communications to protest towns targeted by operations, he added. Taranco spoke of reports of summary executions and soldiers defecting because of a shoot-to-kill policy, diplomats said.
In a bid to keep Syria high on the Security Council agenda, Western nations pressed for a new report next week with briefings from the top UN human rights and humanitarian officials.
Envoys from Britain, France, Germany and Portugal said after the meeting that the Security Council would have to consider "further action" if events did not improve by the next report.
Taranco's briefing was "depressing and chilling," Britain's deputy UN ambassador Philip Parham told reporters.
He said the council had been told that "gross human rights violations" had become a central feature of the crackdown, while there was no prospect of progress so long as the security operation continues and mass arrests are carried out.
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"If the Syrian regime persists in ignoring the demands of the international community, which are not just the demands of the Security Council, which are growing and becoming more urgent from the region, then we will have to consider ways to increase pressure on the Syrian regime," added France's deputy envoy, Martin Briens.
US Ambassador Susan Rice took the increasingly tough line of President Barack Obama's administration into the debate.
Assad has met "calls for change with cruelty and contempt," she told the meeting. Thousands of innocent people had been "killed in cold blood" and "Assad has breached the most basic rules of diplomacy by sending thugs to attack diplomatic missions."
Rice said the United States and Europe were bringing "greater pressure to bear on the Syrian regime through further coordinated diplomatic and financial measures."
The United States was also trying to halt the supply of weapons and ammunition to Syrian security forces.
Russia's UN ambassador Vitaly Churkin said US calls for sanctions were not helpful.
"We are urging restraint, reform and dialogue," Churkin told reporters.
"What we are telling them (Syria) is that they need to have serious reforms," he said while criticizing the Syrian opposition for not entering into dialogue with the Assad government. He also insisted there were "some encouraging signs."
Syria's UN Ambassador Bashar Jaafari accused European envoys of misleading the media and public with their figures on the death toll and thousands of arrests. He sparked the fury of British diplomats by comparing the unrest in his country to riots roiling Britain.
Western nations have hailed the growing condemnation of Assad from the region, including the Gulf Cooperation Council, the Arab League leader and influential nations such as Saudi Arabia that have withdrawn their envoys.