The Lebanese Armed Forces say they have launched the third phase of a broad offensive to capture areas controlled by the Islamic State group on the border with Syria.

The army began its operation on Saturday and has so far captured about two-thirds of the area once held by IS.

The army said in a statement that a Lebanese mine expert was killed and four others wounded early Tuesday when explosives left behind by the extremists went off as they dismantled them.

The Syrian army and its ally, the Lebanese Hezbollah group, have launched a simultaneous operation to clear IS militants from the Syrian side of the border in the western Qalamoun mountain range. Hezbollah has been fighting in Syria alongside President Bashar Assad's forces since 2013.