Warring rebel factions in Syria have joined together to fight off an assault by a powerful Islamist group which launched an attack on rebels this week.

The hardline Jabhat Fateh al-Sham, once allied with al Qaeda and formerly known as the Nusra Front, attacked Free Syrian Army (FSA) groups west of Aleppo this week, accusing them of conspiring against it at peace talks in Kazakhstan this week.

Ahrar al-Sham, which presents itself as a mainstream Sunni Islamist group, sided with the FSA groups and said Fateh al-Sham had rejected mediation attempts. The Ahrar statement said that any attack on its members of was tantamount to a "declaration of war", and it would not hesitate to confront it.

Rebel factions Alwiyat Suqour al-Sham, Fastaqim, Jaish al-Islam's Idlib branch, Jaish al-Mujahideen and al-Jabha al-Shamiya's west Aleppo branch said in a statement they had joined Ahrar al-Sham.