Three people were killed when Syrian mortars hit villages in northern Lebanon on Tuesday, as violence in Syria continued to spill across the border.
Residents said they had been under fire for five hours overnight, and that there had been sporadic shelling in the area for days.
One Lebanese man was killed by the shelling, and two Syrians living in Lebanon died when they were hit by a car speeding away from an area under fire, residents told Reuters.
It was the second fatal attack in three days. Three people were killed by mortar fire from Syria at the weekend and President Michel Suleiman ordered an investigation.
Rebels in Syria's 16-month-old uprising against President Bashar al-Assad have been operating out of border zones, and tension are high on Syria's Lebanese and Turkish frontiers.
But Lebanon, with a history of domination by its powerful neighbor, is anxious to avoid being drawn in to the uprising, and its reaction to cross-border incidents has been more restrained than Turkey's.
Lebanon's cabinet on Monday approved reinforcement of the army along the Syrian-Lebanese border due to rising violence, but residents said they had yet to see an increased security presence.
In the border town of Wadi Khaled, a Reuters witness saw at least five buildings damaged, some of them set ablaze by the shelling.
Many residents of the border area are leaving their homes and heading to Lebanon's port city of Tripoli to escape the violence, locals said.
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