World leaders voiced fears that Syria stands on the brink of civil war as the UN Human Rights Council ordered an independent probe to hunt those guilty of the Houla massacre.
The Syrian Observatory for Human Rights, meanwhile, said at least another 45 people, including 12 soldiers and eight people in the Damascus region, were killed in relentless violence across the country.
In Geneva, the Human Rights Council ordered an independent probe to hunt those guilty of the massacre in Houla that rights chief Navi Pillay said could constitute a "crime against humanity".
Forty-one of the 47-member council backed a call urging an investigation by the Commission of Inquiry on Syria, set up by the council last year to gather evidence on alleged rights abuses.
Russia, China and Cuba voted against the resolution which they said was "unbalanced" as it presumed the guilt of the Syrian authorities for the May 25 massacre of 108 people, mostly children and women, in the town of central Syria.
Talks in Berlin between German Chancellor Angela Merkel and Russian President Vladimir Putin exposed the sharp differences between Arab and Western governments and Damascus allies Beijing and Moscow on the way forward.
The two leaders found common ground on backing the peace mission of UN-Arab League envoy Kofi Annan but the former UN chief himself admitted to frustration at the slow progress he was making in staunching the bloodshed.
Security forces opened fire on demonstrators in several towns amid protests across the country against the Houla killings, activists said.
UN officials have said the Houla massacre was the result of army shelling followed by a ground assault by loyalist militia. A Syrian government inquiry blamed rebel fighters.
After his talks in Berlin, the Russian president acknowledged that Syria could be teetering on the edge of civil war but underlined his opposition to military intervention to stop the bloodshed.
"You cannot do anything by force," Putin told reporters.
He also hit back at suggestions Moscow was supplying arms for use in Syria. "As far as arms supplies are concerned, Russia does not supply the weapons that could be used in a civil conflict," Putin said.
US Secretary of State Hillary Clinton, however, charged that Russia has continued to supply arms to the regime of Syrian President Bashar al-Assad.
"We know there has been a very consistent arms trade, even during the past year, coming from Russia to Syria" and that this had strengthened the Assad regime, she said in Oslo.
"The fact that Russia has continued to sustain this trade in the face of efforts by the international community to impose sanctions ... has raised serious concerns on our part," she said.
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In Moscow, the foreign ministry blamed the Houla massacre on foreign assistance to Syrian rebels, including arms deliveries and mercenary training.
"The tragedy in Houla showed what can be the outcome of financial aid and smuggling of modern weapons to rebels, recruitment of foreign mercenaries and flirting with various sorts of extremists," the ministry said.
Speaking in Lebanon, Annan spoke of his frustration at the slow progress in implementing his six-point peace plan that was supposed to begin with a ceasefire from April 12 but that has been violated daily.
The Syrian Observatory says as many as 2,300 of the more than 13,400 people killed since the uprising against Assad's regime began in March last year have died since April 12.
Twelve soldiers were killed in fighting on Friday in Idlib province of northwest Syria and in Daraa in the south, the monitoring group said.
"We are all impatient and frustrated over the violence, over the killings. I am frustrated even more maybe than most of you," said Annan.
"Bold action has to be taken by President Assad in Syria to put real energy into the implementation of the six-point peace plan."
But the rebel Free Syrian Army said the Annan plan had failed and announced that it will resume "defensive operations" after the expiry of a noon (0900 GMT) ultimatum for the regime to adhere to the plan.
FSA spokesman Kassem Saadeddine told AFP that "we will not go on the offensive because we do not want to be singled out as the ones responsible for breaking the peace initiative."
"The Annan plan has failed," he said. "The ball has been in the regime and international community's court from the start, and the initiative was a failure from the day it was signed."
Meanwhile, reports emerged of the summary execution of 12 civilians at an army checkpoint in another central town on Thursday.
"The workers were on a bus when they were forced to stop at a checkpoint on the outskirts of Qusayr," said Salim Kabbani of the Local Coordination Committees, which organises protests on the ground.
"Regime forces tied their hands behind their backs and shot them."
China's ambassador to the United Nations in Geneva Liu Zhenmin told the rights commission meeting that an immediate ceasefire was necessary, otherwise the situation could lead "perhaps even to civil war."
And after talks with UN chief Ban Ki-Moon in Istanbul, British Foreign Secretary William Hague voiced similar concerns.
"Both the secretary general and I -- and also the opposition in Syria -- think that Syria is on the edge of a catastrophic situation ... on the edge of an all-out civil war and the collapse of Syria into sectarian strife," Hague said.