Two rockets struck a mainly Shi'ite town near Lebanon's border with Syria on Monday and security forces blew up a suspected car bomb as they struggled to contain sectarian violence fuelled by a Syrian army offensive across the frontier, Reuters reported.
The rocket attack on Al-Labwa was the latest strike on a Shi'ite target inside Lebanon after Syrian President Bashar al-Assad's forces and their Lebanese allies Hezbollah recaptured the border town of Yabroud from Sunni Muslim rebels on Sunday.
The rebel defeat at Yabroud sent a stream of refugees and fighters across the border towards the Lebanese Bekaa Valley town of Arsal, and was followed hours later by a suicide car bombing against a local stronghold of Shi'ite Hezbollah.
The border area has been steadily sucked into Syria's nearly four-year-old conflict as Syrian troops and jets targeted rebel bases on the frontier and suspected Syrian rebels fired rockets at Shi'ite towns to punish Hezbollah for supporting Assad.
But the rebel loss of Yabroud could exacerbate sectarian tensions across Lebanon and the flight of 2,000 defeated rebels - some of them into Lebanon - would further destabilize the already volatile Bekaa Valley.
Prime Minister Tammam Salam met army chief General Jean Kahwaji on Monday and called on the military to "take all necessary measures to control the situation in Bekaa's border areas", a statement from his office said.
When the two rockets struck Al-Labwa, a mainly Shi'ite town about five miles (eight km) west of the Sunni town of Arsal, gunmen took up positions on the street and others leapt into cars. Reuters journalists in the town heard sirens of emergency vehicles, but there were no immediate reports of casualties.
The attack on Al-Labwa followed a suicide bombing which killed three people in the nearby town of Nabi Osmane on Sunday. Two radical Islamist groups with suspected ties to Sunni al Qaeda militants in Syria claimed responsibility.
At the site of the blast yellow Hezbollah banners were flying on Monday. "Dear criminals, our blood is stronger than your terror," read one of them, next to the group's logo.
The blast blew apart buildings in the area, including a barber shop where the twisted remains of a barber chair were visible through the door. A damaged grey Mercedes was in the road and the twisted charred remains of a car.
One person was killed in the same town on Saturday after several rockets were fired from near Arsal.
Yabroud was the last stronghold of Sunni rebels on the Syrian side of the border and its capture by the Syrian army and Hezbollah triggered open celebrations in Beirut's southern Shi'ite suburb - mixed with fear of imminent revenge attacks.
More than 100 youths on motorbikes paraded through the district on Sunday, waving Hezbollah flags and hooting their horns, and sheep were slaughtered in front of a mosque.
Hours later, however, Hezbollah members deployed in the streets after the Bekaa suicide bombing. Soldiers blocked off entrances to the suburb and there were lengthy queues at the few open checkpoints, where cars were thoroughly searched.
In the Bekaa Valley on Monday the army blew up an explosives-laden car about five km (3 miles) north of Sunday's suicide bomb attack. The twisted and charred remains of the car could be seen in a field of almond trees on the side of a hill on the outskirts of the small town of Fakeha.
Army humvees mounted with machine guns rolled along the crest of the hill and Lebanese soldiers in fatigues patrolled through the fields and the town, taking up positions along roadsides looking for the men who had been driving the car.
Access from Al-Labwa to Arsal was blocked, possibly to prevent Syrian Sunni rebels who may have crossed into Arsal from coming into confrontation with Al-Labwa's Shi'ite population.
"The road into and out of Arsal is cut," Arsal mayor Ali al-Hujeiri told Reuters, adding that more than 400 families arrived in Arsal over the last 48 hours.
He said only a handful of the 100 wounded people who were reportedly treated in an Arsal field hospital were rebels, but that other fighters may have taken refuge in the rugged and remote border region surrounding the town.
In Tripoli the army clashed overnight with fighters who fired rockets at military posts in the northern coastal city, security sources said. Twelve people have been killed in four days of fighting triggered by tensions between Sunni Muslims and minority Alawites, from the same faith as the Syrian president.
In his meeting with the army chief, Prime Minister Salam also instructed the military "to adopt zero tolerance" towards anyone threatening security in Tripoli, Lebanon's second city.