A car bomb Thursday ripped through the main square of Hermel, a Hezbollah bastion in Lebanon's Bekaa Valley, killing three people in the latest attack linked to Syria's war, officials said.
A group calling itself Al-Nusra Front in Lebanon, after a Syrian Al-Qaeda affiliate, said it was responsible for the blast and said it was a suicide attack, in a statement on social media.
A security official told AFP the bomb exploded in front of Hermel's main government building, which houses administrative offices as well as police and security posts.
Health Minister Ali Hassan Khalil said three people were killed and 31 wounded in the town located only about 10 kilometres (six miles) from the Syrian border.
"Two of the bodies were unidentified. We don't know whether one of them was a suicide attacker," Khalil told Hezbollah's Al-Manar television channel.
It was the first bombing to hit Hermel since the Syrian conflict erupted in March 2011, and the fifth major assault on a Hezbollah stronghold in Lebanon since the Iranian-backed Shiite movement admitted it was fighting alongside President Bashar al-Assad's forces in Syria.
"By the grace of God, an earthquake has shaken the bastion of Iran's party in Hermel, in a martyrdom (suicide) attack by one of the lions of Al-Nusra Front in Lebanon," said the statement posted on Twitter.
The attack was staged "in response to the party's crimes against children, women and Sunnis in Syria," it added.
It was not immediately clear if the group is linked to Al-Nusra Front, Al-Qaeda's affiliate in Syria and one of the main groups fighting to topple Assad.
The bombing came as the trial in absentia of four Hezbollah members accused of murdering Lebanese former prime minister Rafiq Hariri in 2005 began at a UN-backed court in the Netherlands.
Interior Minister Marwan Charbel said that "given the human remains in the car and next to it, it seems like a suicide attack, but we will not rush to judgement".
The army cordoned off buildings damaged in the attack as investigations were launched.
"The explosion was huge. People are really scared and upset. It took place just as people were on their way to work and to go about their daily business in the middle of town," said Ali Shamas, the headmaster of a Hermel college.
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An AFP photographer saw body parts strewn on the ground, as well as damaged vehicles and ambulances transporting casualties away.
'Solidarity needed to immunise Lebanon'
President Michel Sleiman described the attack as "the latest in a criminal series that target Lebanon's stability."
"Immunising (Lebanon) from such terrorist groups will require solidarity between leaders and the people, and the rapid establishment of a government that is able to meet the challenges."
For nine months, Lebanon's rival political camps have failed to form a government.
Tensions and deadly fighting linked to the Syria war have also gripped Lebanon, which is sharply divided into pro- and anti-Damascus camps.
Hezbollah has since last May been openly involved in Syria's war, sending in thousands of fighters to support regime forces.
But Hezbollah MP Nawar al-Sahili said: "What happens in Syria stays in Syria... There must be no links made between our presence in Syria and these terrorist, criminal, cowardly explosions."
Five major attacks have struck Hezbollah bastions in southern Beirut and in eastern Lebanon since it admitted it is fighting on Assad's side.
Prior to Thursday's attack, the two most recent were claimed by the Abdallah Azzam Brigades, which is loyal to Al-Qaeda.
Until 2005, Lebanon had been dominated politically and militarily by Syria for 30 years.
While Lebanon has suffered a spike in violence since the war in Syria broke out, the frequency of attacks has risen in recent weeks.
In November, 25 people were killed in a twin suicide attack targeting the Iranian embassy in southern Beirut, also a Hezbollah bastion.
Then in late December, eight people were killed in a car bomb attack targeting a former minister opposed to Assad while five other died in a suicide blast that tore through southern Beirut on January 2.