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In a new communique, Jabhat al-Nusra, al Qaeda’s affiliate in Syria, announced Sunday that it would withdraw from its frontline positions against the Islamic State militant group north of Aleppo. The announcement is the latest in a series of developments in Syria’s north and northwest that have scrambled the balance of power there, as Kurdish forces have expanded their control at the expense of the Islamic State.

Both the United States and Jabhat al-Nusra share a common enemy in the Islamic State. But Washington has repeatedly bombed Nusra forces in Syria, and the al Qaeda-linked group has attacked American-trained rebels and last month captured the commander of the Division 30 rebel group, a U.S.-trained force.

Jabhat al-Nusra now claims that it has no choice but to abandon its positions in the northern countryside of Aleppo, as it cannot enter into an alliance with Turkey and the United States. In recent weeks, Ankara and Washington announced they will support the creation of what has been described as a “safe zone,” free of the Islamic State along the Syria-Turkey border. That zone, the details of which remain highly unclear, would include a section south of the border about 60 miles wide, running from Jarablus in the east. Kurdish forces will reportedly not be allowed in that zone, though its fighters control large parts of the Syria-Turkey border.

The establishment of the zone, likely backed in some fashion by U.S. and Turkish forces, would represent a significant escalation in both countries’ involvement in the Syrian civil war.

Jabhat al-Nusra, also known as the Nusra Front, is unwilling to participate in the coalition for three reasons, according to a translation of the statement distributed by SITE Intelligence Group, which tracks online jihadi statements. In its statement, the group argued that the zone has more to do with Turkish national security interests — specifically, weakening the Kurdistan Workers’ Party, or PKK — than undermining the Assad regime.

We in the Nusra Front do not believe it is permissible by sharia to enter into this coalition, neither by joining its ranks, nor by relying upon it, and not even coordinating with it.

The decision of the battle now was not a strategic choice that stems from the free will of the militant factions. Rather, its first aim is the national security of Turkey, and we also do not believe it serves the interest of the battlefield now, especially after the Nusayri [Assad] regime is rattled and the mujahideen have reached its strongholds on the Syrian coast.

The fighting groups and factions in the land of Syria have the ability to fight the renegades [Islamic State] if they united and joined — within the sharia ways and means — and adhered to the Rope of Allah the Almighty, without having to rely on regional or international forces.

Jabhat al-Nusra’s withdrawal from the battle north of Aleppo also is indicative of the shortage of effective fighting ground forces inside Syria to combat the Islamic State. Moreover, it creates a vacuum that other militant groups, including the Islamic State, could exploit.