Beirut- Syrian rebels have killed 15 members of the security forces in an ambush as a human rights organisation accused Damascus of war crimes.

The Britain-based Syrian Observatory for Human Rights that had been tracking the 14-month-old uprising against President Bashar al-Assad made the allegation on Wednesday.

It said two rebel militias also died in clashes that followed the ambush in the northern province of Aleppo.

State media carried no news of the attack, the latest in a series of heavy losses inflicted on pro-Assad forces in the past week by some of the disparate militias fighting for his downfall.

Twelve soldiers died in a firefight in the eastern town of Deir al-Zor on Tuesday, the Observatory said, and nine people, including security officials, died in twin suicide bombs in   Idlib on Monday, according to state media.

Most independent media are barred from Syria or have their movements restricted, making it hard to verify such reports.

The UN said Syrian forces had killed 9,000 people in a violent crackdown on mass protests  against Assad in March 2011. The initially peaceful demonstrations turned into a bloody guerrilla insurgency.

Damascus said 2,600 personnel had been killed by “armed terrorists”. Since a UN backed ceasefire came into effect on April 12, it had cited rebel assaults as justification of its right to respond to “any violation or attack”.

The UN now has 30 blue-helmeted monitors inside Syria and this week accused both pro- and anti-Assad forces of violating the three-week-old truce.

On Tuesday it said it had credible reports of at least 34 children had been killed since the ceasefire came into effect. (Reuters/NAN)