A massive suicide car bomb targeting an army checkpoint in the eastern Lebanese town of Hermel near war-torn Syria killed two soldiers and a civilian on Saturday.
The bomb is the third this month to hit areas of Lebanon where the powerful Shiite Muslim movement Hezbollah, which is helping the Syrian regime battle insurgents, is a dominant force.
The Al-Nusra Front in Lebanon, a group named after Al-Qaeda's Syrian affiliate, claimed the bombing on Twitter, indicating it was a revenge attack for Hezbollah's involvement in the Syrian conflict.
The bombing drew condemnation from the United Nations, Lebanese Sunni Muslim leader Saad Hariri and new Prime Minister Tammam Salam, who unveiled a cabinet last month, ending months of political vacuum.
A medical official who spoke to AFP on condition of anonymity said two soldiers and a civilian were killed in the Saturday's attack, and that 16 other people, five of them soldiers, were wounded.
The suicide car blast ripped through the army checkpoint which lies at the main entrance of Hermel in the Bekaa Valley, and at which cars are routinely stopped and searched by soldiers.
Immediately after the attack, military police imposed security measures in Hermel, as they searched for suspects and evidence, said the National News Agency (NNA).
Hezbollah-dominated parts of eastern Lebanon and southern Beirut have been hit by a wave of violent attacks in recent months, since the Shiite group acknowledged it sent fighters to Syria.
But until Saturday, the attacks had only killed civilians.
Hezbollah television channel Al-Manar broadcast amateur footage showing a huge fire over the checkpoint, and people screaming in the background.
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- 'Act of terrorism' -
Prime Minister Salam condemned the attack as "an act of terrorism," the NNA reported.
Salam also called on the Lebanese to "rally around the army and the security forces, which have always been and will continue to be a fortress for the nation."
His government brings together Hezbollah and its allies with the Sunni-led bloc of former premier Hariri, who back opposing sides in Syria's war.
The nearly three-year conflict has deeply divided Lebanon and seen violence spill over into the country, which is also hosting nearly a million refugees from its war-wracked neighbour.
Hariri also called the bomb a "terrorist" act.
UN Special Coordinator for Lebanon Derek Plumbly also denounced the deadly bombing.
"The recurrence of acts of terrorism should only strengthen the support of all Lebanese for the institutions of the state, particularly the army and the security forces, as they work to safeguard Lebanon's security and stability," he said in a statement.
Saturday's blast comes just four days after three people died in a twin bomb attack targeting the cultural centre of Hezbollah backer Iran in Beirut.
It also comes two weeks after a bombing at petrol station in Hermel run by a Shiite charity killed four, an attack also claimed by the Al-Nusra Front in Lebanon.
While Hezbollah has been the main focus of a string of attacks, many of them claimed by radical Sunni groups that oppose the Shiite movement's role in Syria, the army has also been a target.
Extremist Sunnis see the army as taking the side of Hezbollah and other Assad allies in Lebanon's violence, which has escalated in recent months as a result of Syria's conflict.