Civilians, at 24,964, represented the vast majority of those killed, said the Syrian Observatory for Human Rights, which counts as civilians non-military fighters who have taken up arms against President Bashar al-Assad.

It said the balance consisted of 8,767 soldiers and 1,276 military defectors.

"In addition, we have documented the deaths of 422 other people whose identities we were unable to verify," said Observatory director Rami Abdel Rahman.

In addition to excluding unidentified victims, the Observatory does not include thousands of people who are missing. Some are thought to be in detention and others dead.

It also excludes thousands of pro-regime militiamen.

The Observatory relies on a network of activists, lawyers and medics inside Syria for its information.

The uprising began as pro-reform protests but morphed into an armed insurgency after the government began brutally crushing demonstrations.