At least 17,129 people have been killed in Syria's 16-month-old revolt against President Bashar al-Assad, the Syrian Observatory for Human Rights said, according to Reuters.

The pro-opposition Observatory said at least 11,897 of them were "civilians" - but added it could not determine how many of those might have been fighters who had joined an insurgency led by army defectors.

Around 884 defectors have been killed in the crackdown on the protest movement that began in spring 2011 and has since turned into an armed rebellion, the Observatory said.

The total death toll included members of the security forces still loyal to Assad, of whom 4,348 have died, it said.

Syrian authorities have said in the past that more than 2,600 members of the security forces have been killed, but have not given a death toll for several months.

United Nations officials said in April more than 10,000 people had been killed in the violence but have offered no estimates since.

The Observatory is based in Britain and has a network of activists across the country. Independent journalists and aid groups are severely restricted by Syrian authorities and figures are impossible to verify.

Bloodshed has intensified in Syria in recent weeks, with around 100 people being killed daily. (