Violence across Syria has killed at least 31,022 people, most of them civilians, since the outbreak of an anti-regime revolt in March last year, a monitoring group said. "At least 22,257 civilians, 7,578 soldiers and 1,187 defectors have been killed in violence in the past 18 months," Syrian Observatory for Human Rights director Rami Abdel Rahman told Agence France Presse. September saw at least 4,727 people killed, including 305 on September 26 alone -- the bloodiest single day since the conflict began, according to the Observatory. The highest monthly toll came in August, when the watchdog recorded 5,440 victims. The Observatory's civilian toll includes non-military defectors who have taken up arms against the regime of President Bashar Assad. But the tallies do not count the many unidentified victims of the bloody conflict. "Our count excludes hundreds of bodies found in towns and cities across Syria, but whose identities we have been unable to confirm," said Abdel Rahman. "It also excludes thousands of people missing in detention, and thousands of shabiha (pro-regime militiamen) whose deaths are impossible to document." The Britain-based Observatory relies on a network of activists, lawyers and medics in Syria for its information. "We fear that the actual number may be higher, as both the regime and the rebels are concealing some of the deaths among their ranks," Abdel Rahman said. The revolt began as a peaceful uprising but developed into a bloody insurgency after calls for reform were met with bloody regime repression.