President Bashar al-Assad's forces killed at least 27 people on Wednesday in fighting to fend off a rebel advance on a Syrian military air base near the Lebanese border, opposition campaigners said.
Rebel fighters breached defences of the Qusair Air Defence Base, located some 14 km (nine miles) from Lebanon's Bekaa Valley, a stronghold of the pro-Assad Lebanese Shi'ite movement Hezbollah, after a one-month siege, activists in the area said.
But the army countered with rockets and aerial bombings on rebel-held areas in the vicinity, the source said.
Video footage taken by activists in a makeshift clinic showed a man weeping over bodies of members of his family they said were killed by an army rocket attack on the nearby village of al-Bouaida al-Sharqiya.
Among them were two girls, one with a leg blown off and her head partly missing and another girl wrapped in a blanket and her head covered in a white scarf.
"Leave me, leave me," the man cried as he embraced the body of one of the girls, while other men tried to pry him off the body.
Opposition activist Nader al-Husseini said the base, which has a runway but no active planes, was an important rebel target because it is being used to bomb the surrounding countryside.
He said rebel fighters appear to have entered the perimeter of the base but troops were firing back.
The Qusair farming area is a key supply line from Lebanon for opposition fighters in the city of Homs to the north.
Opposition military sources say the army has been seeking to recapture several towns along the routes from Homs to Qusair to cut off the supply line.
Homs, Syria's third largest city, is also strategic because it controls access to the routes between bases on the Mediterranean coast and Assad's core forces in Damascus.
Most of Homs' inhabitants have fled since the uprising against Assad's autocratic rule began two years ago. The war-torn city has become completely segregated between Sunni Muslim areas and neighborhoods controlled by members of Assad's minority Alawite sect, an offshoot of Shi'ite Islam.