The UN’s Human Rights Council on Friday condemned Syria for the Houla massacre and ordered an investigation into the killings.
Forty-one countries at the 47 member Geneva-based forum backed the motion.
China, Cuba and Russia voted against, while two abstained and another member was absent.
Evidence gathered by the probe could form the basis for a prosecution at the International Criminal Court in The Hague.
The bloodbath is a clear breach of a ceasefire deal brokered by international envoy Kofi Annan in April.
Earlier on Friday, UN Human Rights Commissioner Navi Pillay had called for Syria to be prosecuted. She said the atrocities “may be crimes against humanity”.
“Those who order, assist, or fail to stop attacks on civilians are individually criminally liable for their actions,” Pillay said. “Other states have a duty to do all they can to prevent and prosecute perpetrators of international crimes.”
On Thursday, a Syrian government investigation blamed “terrorists” seeking to trigger foreign military intervention.
UN orders probe into Syrian bloodbath