Three Lebanese soldiers were killed during an offensive to take back areas along the Syrian border from Islamic State, the military said Sunday.

A landmine exploded under one of the advancing armored vehicles of the army a day after it launched its biggest military operation yet against IS.

“An army vehicle was hit by a landmine on the al-Ajsa road roundabout in Jurud Arsal at noon today, killing three soldiers and injuring one soldier seriously,” the army said in a statement, according to the French news agency, AFP.

The casualties were reported a day after the army began its operation against IS in the Jurud Ras Baalbek and Jurud al-Qaa areas a mountainous region bordering Syria.

Simultaneously, the Syrian army, along with its ally the Lebanese Hezbollah group, pushed to clear Islamic State militants from the Syrian side of the border.

Islamic State gained a foothold along the small Mediterranean country’s border with Syria in 2014.