Islamist fighters in Syria have joined forces to form what may be the biggest rebel army in the country, further undermining Western-backed military commanders and potentially challenging al-Qaeda.

The announcement yesterday of a common leadership for the Islamic Front, an amalgam of six major Islamist groups which had earlier declared an intention to merge, coincided with accounts of a battle on the Turkish border between rival Islamists that ended with al-Qaeda allies taking control of the town of Atma.

Factional fighting and fragmentation among those seeking to overthrow President Bashar al-Assad have hampered the revolt and the latest effort to unite has yet to show that it can result in effective coordination among groups which between them control large parts of Syria and some tens of thousands of fighters.

Gains by Assad since the US held back from intervening following a poison gas attack on rebel territory in August have both hardened many rebels against the Western-backed Free Syrian Army (FSA), notionally charged with coordinating the war, and also galvanised some major formations to come together.

Ahmed Abu Eissa, leader of the Suqour al-Sham brigades, was named head of the Islamic Front, members of other groups said.

In announcing its formation in a video statement broadcast on Al Jazeera, Abu Eissa said: “This independent political, military and social formation aims to topple the Assad regime completely and build an Islamic state where the sovereignty of almighty God alone will be our reference and ruler.”

His deputy was named as Abu Omar Hureitan of the Tawheed Brigades, another large Islamist formation which spearheaded a rebel offensive in Aleppo last year. Other groups joining the alliance were Ahrar al-Sham, Liwa al-Haq and the Islamic Army.

The Islamic Front may challenge the growing influence of two big rebel groups linked to al-Qaeda that have drawn thousands of foreigners to fight a sectarian war pitting Sunni Muslim rebels against Assad’s Alawites and their Shi’ite Iranian allies. The Islamic State of Iraq and the Levant (ISIL) and the al-Nusra Front are not part of the Islamic Front, though they have cooperated with some of its component groups.

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