Syrian rebels killed at least 80 army soldiers in the weekend, an opposition watchdog said on Monday, in a surge of attacks that followed their threat to resume fighting if President Bashar al-Assad failed to observe a UN-backed ceasefire.     

The Syrian Observatory for Human Rights said local doctors had confirmed the names of 80 dead government soldiers.     

Insurgents told the group they had killed more than 100 soldiers and destroyed some tanks in clashes across Syria, including Damascus and Idlib province in the northwest.     

Some commanders in the rebel Free Syrian Army had announced they would be "free of any commitment" to international envoy Kofi Annan's peace plan if Assad did not end violence by Friday.     

The May 25 massacre of at least 108 people, nearly half of them children, in the Houla area of Homs province dealt a possibly fatal blow to Annan's proposed ceasefire, which was supposed to take effect on April 12, but never did.     

Rami Abdelrahman, the head of the Observatory, told Reuters that many army checkpoints were destroyed in heavy clashes overnight in Idlib province, where many rebels operate.     

"A minimum of four to six checkpoints in the village of Ariha were attacked and destroyed in the last 24 hours," he said.     

The 15-month-old uprising against Assad's 11-year rule began with peaceful protests, but Syria is now slipping into civil war as rebels fight back against a violent government crackdown.    

The United Nations says Assad's forces have killed more than 9,000 people since March, 2011. Syria blames the violence on armed "terrorists" it says have killed more than 2,600 soldiers and other members of the security forces. – Reuters