A Syrian army bombardment of the southern city of Daraa killed 17 civilians, most of them women and children, on Saturday, a human rights watchdog said, as anger grew over a massacre in a central village.
UN observers who visited the village of Al-Kubeir said they witnessed blood on the walls and "a strong stench of burnt flesh," prompting Western governments to launch a push for tough new sanctions against Damascus.
Nine women and three children were among the dead in the pre-dawn bombardment of a residential neighourhood of Daraa, the Syrian Observatory for Human Rights said.
Dozens of people were also wounded in the city, cradle of the uprising against the regime of President Bashar al-Assad which erupted in March last year, the Britain-based watchdog said.
Mobile communications in Daraa were cut off on Saturday morning, it added.
Observatory chief Rami Abdel Rahman said that the bombardment might have been in reprisal for increased rebel attacks on government troops in recent days.
"Rebels have been attacking checkpoints in many areas across the country in the evenings," he said.
Diplomats in New York said Britain, France and the United States would quickly draw up a Security Council resolution proposing sanctions against Syria. "We will move fast to press for a resolution," one UN diplomat told AFP.
More than 20 unarmed UN observers were allowed into Al-Kubeir on Friday, a day after they were shot at and prevented from entering the village.
"Inside some of the houses, blood was visible across the walls and floors. Fire was still burning outside houses and there was a strong stench of burnt flesh," UN spokesman Martin Nesirky said in New York, delivering a grisly account of the visit.
At least 55 people were killed in Wednesday's assault on Al-Kubeir, according to the Syrian Observatory.
UN officials, unable to confirm that toll, have made it clear they believe government forces and allies were behind the attack on the mainly Sunni Muslim village surrounded by an Alawite population loyal to Assad.
"Armoured vehicle tracks were visible in the vicinity. Some homes were damaged by rockets from armoured vehicles, grenades and a range of calibre weapons," Nesirky said.
UN chief Ban Ki-moon told the Security Council that according to preliminary evidence, troops had surrounded Al-Kubeir and militia entered the village and killed civilians with "barbarity".
Damascus denied responsibility and blamed foreign-backed "terrorists," as it has done repeatedly in the past.
Violence on Friday killed at least 68 people nationwide -- 36 civilians, 25 soldiers and seven rebel fighters, the Observatory said. More than 13,500 people have been killed since the start of the uprising.
-- Additional pressure -- International envoy Kofi Annan called for "additional pressure" in the wake of the latest killings.
The former UN chief said he would discuss with US Secretary of State Hillary Clinton "how we can put additional pressure on the government and the parties to get the (UN-Arab League peace) plan implemented".
A UN diplomat, speaking on condition of anonymity, said: "There will be action in the coming days to get a vote on a resolution which includes measures under Chapter VII of the UN Charter -- which would mean sanctions."
Chapter VII allows for sanctions and, in extreme cases, military action. Russia and China, infuriated by the NATO campaign in Libya last year, have vowed to oppose any military intervention.
Leaders of the armed opposition called on the international community to provide them with better weaponry and support.
"Those who claim to support the Syrian opposition should begin by supporting people on the inside of Syria," said Hussein Sayyed, head of the Supreme Council for the Leadership of the Syrian Revolution, speaking by telephone to a meeting in Washington.
As the exiled Syrian National Council prepared to meet in Istanbul later on Saturday to choose a new leader, Sayyed denied that the opposition was too divided to merit foreign support.
"It is unacceptable for the international community to claim that it is withholding its support because of the fracturing of the opposition while the Syrian people continue to be slaughtered," he told the meeting organised by the Rethink Institute.
The SNC, the main exiled opposition umbrella group, has struggled to unite regime critics ranging from liberal academics to Islamists, or to gain full legitimacy with activists and rebels inside the country.
Its meeting in Istanbul on Saturday and Sunday follows the resignation of its first leader, Paris academic Burhan Ghalioun, last month in the face of criticism that he was monopolising decision-making and allowing the Muslim Brotherhood to play too strong a role.