Lebanon's US-backed army on Saturday announced the start of a long-awaited military campaign to clear Isis militants from a remote corner near the frontier with Syria, an offensive that seeks to end a years-old threat to neighbouring towns and villages.

The Lebanese Hezbollah group and the Syrian army announced a simultaneous offensive to clear Isis militants from the Syrian side of the border, in the western Qalamoun mountain range.

The campaign will involve cooperation between the two sides – although Lebanese authorities insist they are not coordinating with Syrian President Bashar Assad's government. Hezbollah has been fighting alongside Assad's forces since 2013.

The announcements were made Saturday by the Lebanese commander Joseph Aoun on Twitter, and the Central Military Media outlet, associated with the Syrian government.

The presence of extremists in the border area has brought suffering to neighbouring towns and villages, from shelling to kidnappings of villagers for ransom. Car bombs made in the area and sent to other parts of the country, including the Lebanese capital, Beirut, have killed scores of people.

The army has accumulated steady successes against the militants in the past year, slowly clawing back territory, including strategic hills retaken in the past week.

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Lebanese President Michel Aoun (no relation to the Lebanese commander) arrived at the defence ministry early on Saturday to monitor the operation.

Lebanon has been spared the wars and chaos that engulfed several countries in the region since the Arab Spring uprisings erupted in 2011. But it has not been able to evade threats to its security, including sectarian infighting and random car bombings, particularly in 2014, when militants linked to al-Qaeda and Isis overran the border region, kidnapping Lebanese soldiers.

Lebanese politicians say Isis controls an area of about 115 square miles between the two countries, around half of which is in Lebanon. The area stretches from the Lebanese town of Arsal and Christian villages of Ras Baalbek and Qaa, to the outskirts of Syria's Qalamoun region and parts of the western Syrian town of Qusair, which Hezbollah captured in 2013.