The Jaish al-Fath, an alliance of Islamist groups led by al-Nusra Front in the al-Qalamoun region, located Northeast of Damascus, has accused Islamic State of treason by providing a list of ISIL's aggressions against al-Nusra Front.
In a recent statement Jaish al-Fath called on all al-Nusra militants to do their best to fight the Islamic State terrorists.
The infighting seems to have flared up after ISIL turned down an al-Nusra demand for support in the war on the Syrian troops, and tried to establish an independent front in the region of Qalamoun.