Fierce battles raged on Saturday in flashpoint areas of the central province of Homs near the Lebanese border, a watchdog said, while six shells launched from inside Syria landed in Lebanon.
One of the shells launched from Syria hit the town of Hermel in eastern Lebanon, a security source told AFP.
Battles also 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, said the Syrian Observatory for Human Rights.
Hours after troops loyal to President Bashar al-Assad's regime seized Radwaniyeh village near rebel-held Qusayr, fresh fighting raged in the area of Tal al-Nabi Mando, said the Observatory.
Tal is important because it is located on a hilltop, giving whoever controls it a strategic advantage.
The Observatory and anti-regime activists on the ground 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," said Qusayr-based activist Hadi al-Abdallah, who spoke to AFP via the Internet.
Meanwhile, a Lebanese security source said a total of six shells launched from inside Syria landed in the Hermel region of eastern Lebanon, a Hezbollah stronghold.
One of them hit the Dawra neighbourhood of Hermel town. Though there were no injuries, town residents quickly closed down their businesses and took shelter in their homes, said the source.
Two other shells hit the Sahlet al-May area, while three others landed in and around the town of Qasr, he added, speaking to AFP on condition of anonymity.
Cross-border shellfire from the Syrian war has regularly hit Lebanon, on occasion killing Lebanese.
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, said the Observatory.
"Regime troops are trying to seize total control of the town of Jdaidet al-Fadl" southwest of Damascus, the group said.
"Sixty-nine people were killed in violence raging there over the past four days," added the Britain-based watchdog, 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.
Since last year, the army has tried to root out rebels positioned southwest and east of Damascus, in a bid to secure the capital.
In southern Damascus, meanwhile, the army renewed shelling on several rebel enclaves, said the Observatory.
Saturday's violence comes a day after at least 157 people were killed across Syria, according to the Observatory.