A car exploded near a Hezbollah post in eastern Lebanon on Tuesday, leaving casualties, the Shiite militant group and a security source told AFP.
Hezbollah's Al-Manar television confirmed the explosion and said an unspecified number of people were wounded in the attack near the Shiite village of Sbuba.
Lebanon has been deeply divided over the war in neighbouring Syria, and has seen rising unrest since Hezbollah announced it had dispatched fighters to aid President Bashar al-Assad's regime in its war on Sunni-led rebels.
Al-Manar said an SUV parked near the Hezbollah post blew up when members of the militia, which controls much of the Bekaa Valley in eastern Lebanon along the border with Syria, approached the vehicle.
The car was packed with 60 kilograms (130 pounds) of explosives and the blast left a crater three metres (10 feet) wide, Al-Manar said.
"Other Hezbollah members rushed to the scene and opened fire, thinking the others had been ambushed, and then helped the wounded," it said.
An AFP photographer saw four burned out vehicles at the post, one of many manned by Hezbollah in the Bekaa, which hosts tens of thousands of Syrian refugees.
Residents told AFP the position was used by the militia as a staging post for its vehicles and fighters, especially those headed to Syria to fight alongside government forces.
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The Lebanese army said the car bombing occurred at 2:50 am (0050 GMT) on the Sbuba-Nabi Mussa road and that military police were investigating.
Lebanon's NNA news agency reported that militiamen of Iranian-backed Hezbollah had already intercepted two car bombs earlier on the same road.
Later on Wednesday, six rockets fired from Syria rained down on the Bekaa town of Hermel, with one hitting an army barracks, wounding two soldiers, according to a military statement.
A security source had earlier said four people were wounded by rockets that struck residential areas in Hermel, another Hezbollah stronghold which has been hit by cross-border rocket fire several times in the past.
Hezbollah been the target of repeated attacks by suspected Sunni hardliners since its leader Hassan Nasrallah confirmed in April that its fighters were in Syria supporting Assad's forces.
Wednesday's rocket attack was claimed by two obscure Lebanese Sunni militant groups which said they had fired 10 military-grade Grad rockets on Hezbollah targets in Hermel in revenge for Iranian and Hezbollah's actions in Syria.
In recent months, blasts have struck Hezbollah targets in both the Bekaa and Beirut.
On November 19, two suicide bombers targeted the Iranian embassy in a Hezbollah stronghold in south Beirut, killing 23 people.