The government in Syria has come under increased international pressure after the United Nations Human Rights Council approved an investigation into the mass killing of civilians at Houla last week.
The resolution opens the way for individuals to eventually face war crimes charges.
The 47-member forum held an emergency session in Geneva on Friday.
The resolution was put forward by Qatar, Turkey and the United States amid international outrage at the killing of 108 people, many of them children, in Houla last week.
It called for an existing UN team of rights investigators to conduct an independent special inquiry and "identify those who appear responsible for these atrocities and to preserve the evidence of crimes for possible future criminal prosecutions".
China, Russia and Cuba voted against the resolution. Russia and China dismissed it as unbalanced and saying UN observers were already investigating the massacre and there was no need for duplication.
Syria's delegation accused terrorists - its term for anti-government rebels - of carrying out the killings and rejected the text as politically motivated interference. It said its own investigation was under way.
UN High Commissioner for Human Rights Navi Pillay said Syrian forces and pro-government militiamen accused of committing the slaughter could face prosecution for crimes against humanity.
She called again for the Security Council to refer Syria to the prosecutor of the International Criminal Court.
It was the fourth time that the top UN rights forum condemned Syria in a special session in a year, raising pressure on President Bashar al-Assad's increasingly isolated government.
Separately, Russia has said that the Syrian government's investigation into the massacre in the region of Houla indicated it was a "well planned action by militants" intent on undermining peace efforts.
US government website claims evidence of civilian attacks
Meanwhile, a United States government website has published what it says is photographic evidence of mass graves and attacks on civilian areas by Syrian government forces.
The website published a series of overhead photos, said to be taken earlier this week by commercial satellite, of an area near the town of Houla.
The images also showed apparent artillery impact craters near civilian areas of a town called Atarib.
The website says there is evidence of artillery deployed near three Syrian towns and attack helicopters allegedly deployed near the towns of Shayrat and Homs.
Damascus has blamed the Houla massacre on the opposition, which President Assad has tried unsuccessfully for 14 months to crush, killing over 10,000 people in the process, according to the United Nations.
