Lebanon sent commando units to the border with Syria to prevent any spillover of its civil war following a crushing victory for President Bashar al-Assad.

Defeated rebels, mostly mojahedin, poured across the border into the Sunni-dominated town of Arsal, which is surrounded by Shi'ite towns defended by Hezbollah fighters.

The nearby Shi'ite town of Labweh was hit by several rockets , which residents said were fired from Arsal.

The road between the two towns has been blocked with sand barriers, guarded by about 20 Hezbollah members.

Lebanese troops patrolled the border area on foot, blowing up an abandoned vehicle rigged with explosives near the village of Fakiha.

The fall of Yabroud, a smuggling hub for the rebels trying to overthrow President Assad, was a major gain for Syrian government troops and their Hezbollah allies.

It was also the Syrian opposition's last stronghold in the vital border area.

The fall followed months of fighting in the mountainous Qalamoun region between government forces and Hezbollah fighters on one side and the rebels, mostly Islamist militant groups, on the other.

Hezbollah fighters have been instrumental to Mr Assad's success on the battlefield and their support appears to have tipped the balance in the government's favour in Yabroud.

Sunni militants have carried out several suicide and car bombings in Shi'ite-dominated towns and suburbs of Beirut that are Hezbollah strongholds in the past weeks, claiming them as revenge for Hezbollah's role in the Syrian war.

The Sunni group Nusra Front in Lebanon claimed responsibility for a car bombing the previous night in Nabi Othman, a predominantly Shi'ite town in the Bekaa Valley that also has a significant Christian community.

It said in a statement on Twitter that the attack, in which two were killed and 14 wounded, was revenge for Hezbollah's support for President Assad and "a quick response" to the fall of Yabroud into Syrian government hands.