Violence between supporters and opponents of Syrian President Bashar al-Assad spilled into the Lebanese port city of Tripoli on Sunday, with two killed and 20 injured.
The fighting, which first erupted on Saturday, was the worst violence in Lebanon since the uprising against Assad began over 14 months ago.
The violence in Tripoli was sparked by the arrest of prominent Islamist Shadi Mawlawi by Lebanese security forces.
His supporters said his arrest was partly due to his association with Syrian refugees, who have flooded the city since the conflict began.
The port has long been a center of violence in the country, with Sunni Muslims, Salafists and Alawites -- the sect to which the Assad regime belongs -- frequently clashing.
The Lebanese clash came as rebels in Syria claimed to have killed 23 government troops around the town of Rastan in northern Syria on Monday.
Shells and rockets have been hitting the town since 3 a.m. (midnight GMT) at a rate of one a minute. Rastan has been destroyed, a member of the rebel Free Syrian Army (FSA) in Rastan who declined to be named told Reuters by satellite phone.
According to rebels, they destroyed three armored personnel carriers and seized two others, Reuters reported.
Rastan lies about 110 miles north of Damascus.
On Friday the Syrian government appealed to the United Nations for help in combating terrorism, saying that a spate of bombings prove that it is under attack from forces armed by foreign powers.
State media said Assad's regime called on the UN Security Council and UN secretary-general Ban Ki-moon for assistance in tackling the escalating crimes committed by terrorists receiving help from abroad.
The call for aid came after last week's twin car bombing in Damascus that killed at least 55 people and wounded 372, the deadliest attack in Syria since the uprising against Assad began last March.