At least 15 people were killed on Tuesday across Syria in clashes between regime forces and rebel troops, including near the border with Lebanon, the Syrian Observatory for Human Rights said.
The Britain-based group said nine of those killed were civilians, among them one man who died in intense clashes near the central town of Qusayr, near the border with Lebanon.
Officials said the clashes spilled over into Lebanon as Syrian troops chasing rebels made a brief incursion into a sparsely populated area of Lebanon's eastern Bekaa region.
One Lebanese official, who requested anonymity, said Syrian troops briefly entered the Lebanese side of Masharii al-Qaa, a remote region that straddles both countries.
He said one house in the area was hit by mortar rounds and gunfire. Its residents had fled shortly beforehand, he added
Another local resident said several houses were hit.
The border between both countries is poorly demarcated and residents on both sides travel freely across on a regular basis.
Syrian troops have made several brief incursions into Lebanon since the outbreak of the revolt against the regime of Bashar al-Assad a year ago.
A spokesman for Syrian refugees in Lebanon, Ahmed Moussa, told AFP that 75 families had crossed into the eastern Bekaa on Monday.
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An AFP correspondent saw three mini-vans filled with women and children fleeing the fighting in Qusayr.
Fierce clashes were also taking place on Tuesday in Saraqeb, in the northwest province of Idlib, where there were unconfirmed reports that 21 local residents detained by regime forces had been killed, the Observatory said.
Most of Saraqeb's residents have fled the town in recent days in the face of a fierce assault by regime troops seeking to stamp out insurgents in the area.
"Armed rebels have withdrawn from the town after attacking two security posts," the Observatory said.
In Deir Sanbal, also in Idlib province, two soldiers were killed in clashes with rebels.
In Damascus province, heavy gunfire was reported in fields between the capital's Qadam neighbourhood and the town of Daraya, the Observatory said.
One woman was killed early Tuesday by a stray bullet in the Damascus suburb of Douma and two other women died in Maaret al-Numan in Idlib province.
Another four people were reported killed elsewhere across the country.
The uprising in Syria began as a popular revolt in March of last year but has transformed into an insurgency that many fear will lead to a full-blown civil war.
Monitors say close to 10,000 people, the majority of them civilians, have died in the revolt against Assad's regime.