"Seven civilians were killed and 15 wounded in a Syrian regime air strike on the town of Hammuriyeh," said Rami Abdel Rahman, who heads the Syrian Observatory for Human Rights.

Another 20 were wounded in government air strikes on two other towns, as artillery fire hit other parts of the Eastern Ghouta region, he said.

The rebel-controlled enclave has faced escalating bombardment in recent days, with 80 civilians killed on Tuesday, including 19 children.

"This was the highest civilian toll in Syria in nearly nine months, and one of the bloodiest days for Eastern Ghouta in several years," Abdel Rahman told AFP.

Home to an estimated 400,000 civilians, the Eastern Ghouta region has been included in a de-escalation deal that was meant to bring calm.

More than 340,000 people have been killed and millions displaced since the conflict in Syria erupted in March 2011.