The Nusra Front has launched an assault on rival Islamic State positions in the Qalamoun mountains on the Lebanon-Syria border, al-Qaeda’s official representative in Syria said.

According to social media accounts belonging to Nusra, its militants began attacking IS positions on Tuesday and now plan to “eradicate” IS in the region because it has exploited “the vision of an Islamic state”.

While the two groups have clashed throughout much of Syria, they had, until recently, fostered relatively good relations in Qalamoun, a mountain range key to securing supply routes into Syria.

Both IS and Nusra are believed to have been behind previous assaults on the Lebanese town of Arsal.

However, Nusra has now said that IS, which split from al-Qaeda in 2013, has become little more than a collection of "bandits and thieves".

It claimed that all IS militants who it had previously seen eye-to-eye with had either been killed or purged by the IS leadership and accused IS of killing four high-ranking opposition officials with links to Nusra and allied groups, and also of kidnapping rival militants at its checkpoints.

“A decision has been made by the working factions to eradicate this corruptive group because there is no longer any other option, and Allah be the helper,” the statement by Nusra said.

بيان #جيش_الفتح_القلمون بخصوص خيانة داعش للثوار وخاصة خيانتهم للثوار عدن قتال مرتزقة حزب اللات#المركز_الاعلامي_الحر pic.twitter.com/5JerWy5qpK — المركز الاعلامي الحر (@MediaCenterfr) May 12, 2015

The statement added that Nusra did not believe in fighting other al-Qaeda inspired groups, but that it had been left "little choice" as there were no longer any IS members who showed “loyalty to all Muslims”.

Nusra notoriously broke with IS in February 2014 and has since routinely criticised it for its harsh tactics against civilians. On Tuesday, Nusra published a video claiming to show two children who had been conscripted to fight with Islamic State in Qalamoun, north-east of the Syrian capital Damascus.

In the two-minute recording, two young boys wearing helmets say they are 13 years old, and have been fighting with IS for two months.

Speaking in front of a flag reading “al-Qaeda in the Levant,” the boys say they were captured by the al-Qaeda affiliate when they were part of an attempt to attack one of the group’s bases.

The video’s caption alleges that “the state of [IS leader] al-Baghdadi recruits Muslim children by tempting them with money to fight jihadists”. The video’s caption alleges that “the state of [IS leader] al-Baghdadi recruits Muslim children by tempting them with money to fight jihadists”. Nusra has likewise been accused of serious abuses including the execution of hostages, which Human Rights Watch said might amount to crimes against humanity.

Nusra’s pledge to “eradicate” IS comes despite recent gains made by Hezbollah forces and Syrian government troops in the region. The two launched an offensive earlier this month to try and drive out groups like Nusra which has been rolling back forces loyal to Syrian President Bashar al-Assad in much of northern Syria.

On Tuesday, Hezbollah, which is fighting alongside Assad, reportedly made further advances capturing the Syrian town of Ras al-Maara and the eastern outskirts of the Lebanese village of Nahleh.