The Wednesday clash was the first such engagement since the radical Takfiri militants including terrorists affiliated to the so-called Islamic State of Iraq and the Levant (ISIL) withdrew from the town of Arsal three weeks ago following five days of deadly battles with the army.

The army opened fire with artillery after observing suspicious movement by the militants, the source said. There was no immediate information on casualties.

The five-day battle in Arsal marked the biggest spillover to date of the Syrian civil war into Lebanon. Dozens of people were killed, including 18 soldiers.

The insurgents are members of the Nusra Front, al-Qaeda's official affiliate in the Syrian war, and ISIL which has seized swathes of territory in Syria and Iraq.

The militant forces withdrew on Aug. 7, taking with them 18 captive soldiers and 15 policemen.

In early April, Syrian conflict spillover has continued with three rockets fired by militants operating in Syria, striking the northeastern Lebanese region of Bekaa Valley.

NTJ/NJF