At least three soldiers were killed when a suicide bomber detonated a car bomb at an army checkpoint in the Lebanese town of Arsal near the Syrian border, Lebanese military sources said.
Four other soldiers were wounded, an army statement said.
The attack was claimed on Twitter by a shadowy group calling itself Liwa Ahrar al-Sunna in Baalbek – Arabic for the Brigades of the free Sunni Muslims – which also vowed more retaliation.
It said the attack was to avenge the death of Sami al Atrash, a suspect wanted in connection with car bombings targeting Lebanon's Shiite militant group Hezbollah.
Atrash was killed on Thursday in a shootout with the army, which had described him as a "dangerous terrorist", at a hideout in Arsal.
After the checkpoint attack the military said more troops had fanned out across the region, which has seen a spillover of the conflict in Syria.
Thousands of refugees from the Syrian conflict are based in Arsal alongside Syrian anti-regime rebels and allied Lebanese fighters, who have fled across the border from a Syrian army advance.
Lebanese Sunni militants accuse the Lebanese army of conspiring with forces loyal to Syria's President Bashar al-Assad and the Lebanese Shiite group Hezbollah, which has sent fighters into Syria to support Assad in his fight against a Sunni-led revolt.
The attack hit just hours after a speech by Hezbollah leader Sayyed Hassan Nasrallah, who said he was protecting Lebanon by fighting in Syria against Sunni militants.
Lebanon has endured rocket and bomb attacks as the Syrian conflict spreads beyond its border, deepening the sectarian rivalry in the country, which suffered its own civil war from 1975 to 1990.
The Lebanese army made further raids Saturday in Arsal, where they have set up checkpoints this month.
Later in the day a woman was killed and her child was wounded when soldiers opened fire on their car after it failed to stop at another checkpoint at the entrance to Arsal town, an army spokesman said.
(FRANCE 24 with REUTERS)
Date created : 2014-03-29