At least five Lebanese soldiers were among six people killed in a clash on Friday between unidentified gunmen and the army on the border with Syria, a security official told AFP.
Several other soldiers were wounded in the fighting, the official said on condition of anonymity. A wanted gunman was among the dead.
The clash occurred at Arsal, a Sunni area near the frontier, and according to the security source "Islamists" were involved. The official did not elaborate.
An AFP correspondent saw ambulances leave Arsal and head for Baalbek, the main town in the east of the country.
A military spokesman contacted by AFP said only that there had been "incidents."
Lebanon's northern and eastern frontiers have seen spates of violence since the March 2011 outbreak of an uprising in Syria against President Bashar al-Assad, including cross-border shelling and gunfights.