Syrian warplanes also raided a rebel-held district in the northern city of Aleppo, killing at least 11 people, and 22 were wounded when mortar rounds slammed into central Damascus, the monitor said.
In Mleiha at least eight fighters, including a rebel commander, were killed in fierce fighting with government forces, said the Britain-based Observatory.
The previous day 22 opposition fighters were killed, said the Observatory which relies on medics and activists on the ground for its reports.
Mleiha is near regime-held Jaramana, which is frequently shelled by the rebels, and yesterday six children were killed in one mortar attack, according to state news agency SANA.
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But the rebel Free Syrian Army is blocking the offensive, he said.
The fighting has forced several families to flee to neighbouring areas, he said, adding that "Iraqi militiamen" are backing the loyalist army. His comments could not be independently verified.
In Damascus mortar rounds rained down on two districts today, wounding 22 people, said SANA which blamed "terrorists" -- the regime term for rebels.
Meanwhile the death toll from air raids on the Aleppo rebel-held district of Shaar rose to 11, the Observatory said, after reporting only two killed.
Hundreds of people, mostly civilians, have been killed in air strikes on rebel areas in Aleppo since the regime launched a major aerial offensive on the northern city in December.