Lebanon's army said Tuesday it had captured most of a mountainous area on the border with Syria during an operation to clear Islamic State group jihadists from the region.

The army began its campaign in the Jurud Ras Baalbek and Jurud al-Qaa areas on Lebanon's eastern border on Saturday, capturing more than two thirds of the 120 square kilometres held by IS jihadists in the first two days.

"We have captured around another 20 square kilometres, so we have about another 20 square kilometres to go," said army spokesman Brigadier-General Ali Qanso.

He declined to be drawn on how much longer it would take the army to finish the operation.

Four Lebanese soldiers have been killed since the campaign began, including one on Tuesday when a landmine detonated under his vehicle.

The other three were killed when they drove over a landmine at the weekend.

At a press conference, Qanso presented pictures of IS weapons, ammunition and mines recovered during the fight, as well as tunnels used by the jihadist group.

The army estimated that around 600 IS fighters were in the area on the eastern border, where jihadists have long posed a security threat.

In 2014, they invaded the border town of Arsal, capturing 30 Lebanese soldiers and police.

Four were executed by their captors and a fifth died of his wounds. Sixteen were released in a prisoner swap in December 2015, but another nine soldiers are believed to remain in IS hands.

Their fate remains unclear, and Qanso said the soldiers were the army's "top concern".

The army's operation comes after Lebanese militant group Hezbollah carried out its own six-day campaign against fighters from a former Al-Qaeda affiliate further south on the border area.

That offensive ended with a ceasefire under which 8,000 refugees and jihadists were transported to northwestern Syria in return for the release of five captured Hezbollah fighters.

Hezbollah and the Syrian army launched their own simultaneous attack against IS from the Syrian side of the border on Saturday, but Lebanon's army insists it is not coordinating the assault.

Hezbollah is a key ally of Syria's government and has bolstered its forces against rebels there.

source: AFP