A Turkish attack on Kurdish-led forces in northeast Syria would spark a "big war" if U.S. efforts fail to block Ankara's plans, a top Kurdish official told Reuters on Wednesday.

Badran Jia Kurd also said most forces would have to deploy to the border with Turkey in case of attack, and could no longer hunt Islamic State sleeper cells or guard thousands of IS prisoners.

NATO allies Ankara and Washington have been deadlocked for months over a planned "safe zone" in northeast Syria. They agreed on Wednesday to establish a joint operation center in Turkey to manage the zone, but neither said if they had overcome two main points of division: how far the zone should extend and who would command forces patrolling it.