A suicide bomber killed himself and three soldiers when he detonated a car bomb at a Lebanese army checkpoint in the border town of Arsal on Saturday, Lebanese security sources said.
Arsal is home to thousands of Syrian refugees but also Syrian rebels and their Lebanese allies who have fled a Syrian army advance on the Syrian side of the border. Three other soldiers were wounded, the sources said.
Lebanese Sunni militants accuse the Lebanese army of conspiring with forces loyal to President Bashar Assad and the Lebanese Shi'ite group Hezbollah, which has sent fighters into Syria to support Assad fight 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.
On Thursday, the Lebanese army killed a suspected Sunni bomb-maker as they raided his house in Arsal. On Saturday, the army made further raids in Arsal, where they have set up checkpoints this month.
Lebanon has endured rocket and bomb attacks as the Syrian conflict spreads beyond its border, deepening sectarian rivalry in the country, which suffered its own civil war from 1975 to 1990.