Geneva: More than 2,900 people have been killed in the six months since the beginning of a crackdown on anti-government protests in Syria, the UN High Commissioner for Human Rights said on Thursday.

"According to the detailed list of names of individuals we've been keeping, the total number of people killed since protests began in Syria now stands at more than 2,900," said Commission spokesman Rupert Colville in Geneva.

Colville said that figure could rise because "quite a lot more people" have been reported missing in Syria since the uprising against President Bashar al-Assad's government in mid-March, and the UN has yet to verify their whereabouts.

Russia and China on Tuesday vetoed a European-backed draft UN Security Council resolution that would have threatened possible action against Assad. Non-permanent members South Africa, Brazil, India, and Lebanon abstained.