The Lebanese army launched an offensive against an Islamic State enclave on the northeast border with Syria, a Lebanese security source said on Saturday, as Hezbollah and the Syrian army announced an assault from the Syrian side of the border.

The Lebanese army was targeting Islamic State positions near the town of Ras Baalbek with rockets, artillery and helicopters, the source said. The area is the last part of the Lebanese-Syrian frontier under insurgent control. “We started advancing at 5 a.m. (0200 GMT),” the Lebanese source said.

The operation by the Syrian army and Hezbollah, an Iran-backed Lebanese group, was targeting Islamic State militants in the western Qalamoun region of Syria, the Hezbollah-run al-Manar television station reported, an area across the frontier from Ras Baalbek.

Last month, Hezbollah forced Nusra Front militants and Syrian rebels to leave nearby border strongholds in a joint operation with the Syrian army.

The Lebanese army, a major recipient of U.S. military aid, did not take part in the July operation, but it has been gearing up to assault the Islamic State pocket in the same mountainous region. A military source said around 500 IS fighters were holed up in the enclave.

Lebanese President Michel Aoun was following the army operation, called “Jroud Dawn”. “Jroud” refers to the barren, mountainous border area between Lebanon and Syria.

Lebanese security sources have previously said the army intends to fight Islamic State in Lebanese territory on its own, in response to suggestions Hezbollah or the Syrian army may help it.

*Reuters