The Lebanese army launched an offensive on Saturday against a Daesh enclave on the northeast border with Syria as the Lebanese Shia group Hezbollah announced an assault on the terrorist group from the Syrian side of the frontier.

The Lebanese army operation got underway at 0200 GMT, targeting Daesh positions near the town of Ras Baalbek with rockets, artillery and helicopters, a Lebanese security source said. 

The area is the last part of the Lebanese-Syrian border under Daesh control.

Lebanon said it was not coordinating with the regime or Hezbollah. "There is no coordination, not with Hezbollah or the Syrian army," Lebanese General Ali Kanso said.

But Hezbollah leader Hassan Nasrallah said the Lebanese army would attack Daesh from its side of the border, while Hezbollah and the Syrian regime would simultaneously assault from the other side.

A commander in the military partnership fighting in support of the Syrian regime said that "naturally" there was coordination between the operations.

Any joint operation between the Lebanese army on the one hand, and Hezbollah and the Syrian regime on the other would be politically sensitive in Lebanon and could jeopardise the sizeable US military aid the country receives.

Washington classifies the Iran-backed Hezbollah as a terrorist group.

Relations with the Syrian regime

Last month, Hezbollah launched attacks against Syrian opposition groups near border strongholds in a joint operation with the Syrian regime.

The Lebanese army did not take part in the July operation, but it has been gearing up to assault Daesh in the same mountainous region.

Hezbollah has provided critical military support to the regime during Syria's six-year-long war. 

Critics oppose Hezbollah's role in the war.

Northeastern Lebanon was the scene of one of the worst spillovers of Syria's war into Lebanon in 2014, when Daesh and Nusra militants attacked the town of Arsal.

The fate of nine Lebanese soldiers taken captive by Daesh in 2014 remains unknown.

Shia Hezbollah and its partners have been pressing the Lebanese state to normalise relations with Damascus, challenging Lebanon's official policy of neutrality towards the conflict next door.

US President Donald Trump called Hezbollah "a menace" to Lebanon and the region during a meeting with Lebanese Prime Minister Saad al Hariri in Washington last month, and promised continued US support for the Lebanese army.