The Lebanese army advanced into a border town that was attacked by Islamists in an incursion from Syria at the weekend, finding the bodies of 50 militants, a Lebanese security official said.
The army pounded areas around the town of Arsal with artillery for a third day running in a bid to expel the militants whose incursion into Lebanese territory was the first of its kind since the Syrian civil war erupted three years ago, Reuters reported.
At least 13 Lebanese soldiers have been killed in the fighting, which erupted after the Lebanese security forces arrested a commander of the Nusra Front, al Qaeda's affiliate in the Syrian civil war, on Saturday.
The Lebanese army has described the incursion as a planned attack carried out by Sunni radicals including the Islamic State, an al Qaeda offshoot that has seized large areas of territory in Iraq and Syria.
At least two dozen members of the Lebanese security services - both army and police - have either been taken hostage or are missing. Thick plumes of black and grey smoke billowed from the tops of the hills where Arsal lies.
In a statement, the Lebanese army said it had taken full control of a school that militants had seized during the incursion. It said "a number" of soldiers had been killed and wounded in the fighting.
Arsal is a mainly Sunni town located on the Lebanese side of the border between Syrian government-controlled territory and Lebanese Shi'ite areas sympathetic to Hezbollah, the Iranian-backed group that is fighting in Syria alongside President Bahsar al-Assad's forces.