BEIRUT — Gunmen opened fire on a Lebanese army position at the border with Syria on Thursday near a town seized by “Islamic State” insurgents earlier this month, triggering an exchange of fire, a security source said.

The fighting, which erupted before dawn, was still raging in late afternoon, with troops shelling the gunmen who had taken up position on the outskirts of the town.

The Lebanese army had shelled militant positions in the border zone with Syria on Wednesday, a security source said.

It was the first such engagement since the militants, including members of IS, withdrew from the town of Arsal three weeks ago following five days of deadly battles with the army.

The army had opened fire with artillery after observing suspicious movement by the militants, the source said.

There was no immediate word on casualties but an AFP correspondent saw a wounded soldier being evacuated in a military vehicle as plumes of black smoke billowed into the sky over the town.

Earlier, Syrian warplanes had bombed the same area, the source said.

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

The militant forces withdrew from Arsal on August 7 after abducting dozens of members of Lebanese security forces.