Fierce battles raged on Saturday in flashpoint areas of Syria's central province of Homs near the Lebanese border, a watchdog said, adding that six shells fell across the border in Lebanon.
One of the shells hit the town of Hermel in eastern Lebanon -- a stronghold of the Hezbollah -- the first time violence from Syria spilled over into the town, a Lebanese security source told AFP.
Earlier troops loyal to President Bashar al-Assad's regime seized Radwaniyeh village near the rebel-held town of Qusayr in Homs province and hours later fresh fighting raged in nearby Tal al-Nabi Mando, the Syrian Observatory for Human Rights reported.
Tal is important because it is located on a hilltop, giving whoever controls it a strategic advantage.
The Britain-based Observatory said those fighting insurgents were regime troops, pro-regime militiamen and fighters loyal to powerful Lebanese Shiite movement Hezbollah, which supports Assad's regime.
"The situation here is very bad. They are trying to take control of the countryside surrounding Qusayr, in order to then attack us in the city," Qusayr-based activist Hadi al-Abdallah told AFP via the Internet.
The Lebanese security source said the six shells were fired from Syria and hit the town of Hermel and its countryside, causing no injuries.
One shell fell in Hermel's Dawra neighbourhood while two hit the Sahlet al-May area on the outskirts and three others fell in and around the nearby town of Qasr, the security source said.
The shells triggered panic and residents rushed to take cover indoors as shops in Hermel closed.
"The situation is unbearable. The (Lebanese) army should respond to the sources of fire. People are frightened," said Ali Shamas, a 50-year-old school principal from the town.
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In the past two years, cross-border shellfire from Syria has regularly hit Lebanon. Most shells were launched from regime-held areas, but anti-Assad rebels last week claimed firing into Hermel's countryside, threatening further attacks if Hezbollah did not stop fighting the insurgency.
Lebanon is sharply divided over the Syria conflict, with Hezbollah and its allies backing the regime of Assad while the Sunni-led March 14 movement supporting the uprising.
Until 2005, Damascus dominated Lebanon politically and militarily for 30 years.
Elsewhere, battles raged near Damascus, where at least 69 people, many of them rebels, were killed in four days of fighting against government forces in Jdaidet al-Fadl, which the regime is trying to take over, said the Observatory.
"Sixty-nine people were killed in violence raging there over the past four days," it said, citing activists on the ground, who said many were killed in shelling and also in summary executions by the army.
Violence also raged in Sunni areas of the nearby majority Christian town of Jdaidet Artuz, and in rebel stronghold Daraya, scene of fierce fighting for several months.
The opposition Syrian National Council accused the army of staging a "fierce attack" in areas south and west of Damascus.
Jdaidet al-Fadel and other flashpoints are "subjected to a siege and they are deprived of all basic needs for human life", said the SNC.
Since last year, the army has tried to root out rebels positioned southwest and east of Damascus, in a bid to secure the capital.
Saturday's violence left at least 90 people dead, the Observatory said.