At least three Lebanese soldiers have been killed and seven wounded in clashes with gunmen near the Syrian border, the Lebanese army has said.
A military official told Al Jazeera that two soldiers were also missing following the fighting, which began early on Friday morning and continued into the afternoon on the outskirts of Ras Baalbak in the country's east.
"There are martyrs and wounded men among the ranks of the Lebanese army, and we have killed and injured several of the attackers," an army source told the AFP news agency.
The clashes erupted after about 200 gunmen coming from the Qalamun region of Syria attacked a Lebanese military post, a security source said.
The army said in a statement that a "military base in the Ras Baalbek mountains was attacked by a terrorist group".
A security source told the Reuters news agency that soldiers killed at least three of the attackers during the fight.
Syria's civil war has regularly spilled into Lebanon, with fighters briefly overrunning the eastern town of Arsal in August after running gun battles with the army.
The fighters withdrew after a ceasefire, but took with them several dozen hostages from the Lebanese army and police, four of whom have since been executed.
It was not immediately clear which group the attackers belonged to but Syria-based groups such as al-Qaeda's Nusra Front and the Islamic State in Iraq and the Levant (ISIL) have launched attacks in the country in recent months.