UN chief Ban Ki-moon demanded an independent inquiry Monday into the killings of hundreds of civilians in the Syrian town of Daraya as world outrage mounted over the "massacre" by pro-government forces.
Rebels from the Free Syrian Army claimed to have downed a military helicopter as they battled the army in a new front in east Damascus where a human rights watchdog reported at least 35 people killed, among them children.
France said it was working with allies on possibility of setting up buffer zones to protect civilians inside Syria amid growing concern about the plight of fleeing civilians camped out on the country's borders.
The UN chief was "shocked" by the reports of hundreds of bodies found in Daraya, a satellite town southwest of Damascus that was subjected to a five-day assault by pro-government forces last week, his spokesman Martin Nesirky said.
"The secretary general is certainly shocked by those reports and he strongly condemns this appalling and brutal crime," Nesirky told reporters.
"Where hundreds of civilians have been killed in Daraya, this needs to be investigated immediately in an independent and impartial fashion," the spokesman added.
The Syrian Observatory for Human Rights said that 334 bodies had now been found in Daraya after what activists described as brutal five-day onslaught of shelling, summary executions and house-to-house raids by pro-government forces.
The Sunni Muslim town of some 200,000 people is seen as a stronghold of opposition to the minority Alawite-led regime of President Bashar al-Assad.
Grisly videos issued by opposition activists showed dozens of charred and bloodied bodies lined up in broad daylight in a graveyard in Daraya, and others lying wall-to-wall in rooms in a mosque.
State media said the operation had "purified terrorist remnants" in Daraya, while pro-government television Al-Dunia said "terrorists" had carried out the killings.
-- 'Atrocity on a new scale' --
The White House said the reports of the Daraya massacre were the latest evidence of Assad's "wanton disregard for human life."
Britain said it would be "an atrocity on a new scale" and the European Union said it was "totally unacceptable."
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In a new front in east Damascus, rebels from the Free Syrian Army claimed to have downed a military helicopter in the Qaboon district, where activists reported shelling, heavy fire by combat helicopters and fierce clashes between troops and rebels.
State television said the aircraft crashed near a mosque.
The FSA had previously said it shot down a Syrian warplane two weeks ago in the eastern province of Deir Ezzor and captured its pilot, but the claims cannot be independently confirmed.
Heavy shelling and fierce fighting also engulfed the Jubar district of east Damascus as well as several towns outside the capital, the Observatory said.
The Britain-based watchdog said that nationwide a total of 148 people were killed in violence on Monday.
Human rights groups have accused the regime of committing many atrocities during the 17-month conflict and a UN panel said earlier this month it was guilty of crimes against humanity. It also accused the rebels of war crimes.
Activists say around 25,000 people have been killed since the uprising against Assad's rule broke out in March last year, while the United Nations says at least 200,000 people have fled to neighbouring countries and another 2.5 million are in need inside Syria.
Underscoring the growing humanitarian crisis, Turkey, which is struggling to cope with an influx of 80,000 refugees, said another 9,000 were now massed at the border awaiting for more camps to open.
Turkey has called for establishment of protected buffer zones inside Syria to receive people displaced by the conflict and prevent them flooding over the border and French President Francois Hollande said Monday that discussions were under way with allies on the possibility.
"We are working ... (on) the initiative of buffer zones proposed by Turkey," Hollande said, adding: "We are doing so in coordination with our closest partners."
Hollande urged the Syrian opposition to form a "provisional, inclusive and representative" government, adding: "France will recognise the provisional government of the new Syria as soon as it is formed."
But Washington cautioned against moving ahead too rapidly with a provisional government, saying more work needed to be done to ensure that it was broad-based and representative.
State Department spokeswoman Victoria Nuland said that the United States was calling on the opposition "to coordinate more closely" with Syrians both inside and outside the country.
"We would want to ensure that that was based on a solid democratic plan and that it reflected a broad cross-section of those in Syria and reflected the values of inclusion, the values of human rights and protections for all groups," she said.
Some analysts have voiced concern that the opposition is dominated by Sunni hardliners who could seek revenge against Assad's minority Alawite community, threatening prolonged sectarian bloodshed.