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.

Jia Kurd and a second top Kurdish politician said the fruits of U.S.-Turkish talks remained unclear.

“We want a political solution and dialogue,” said Jia Kurd, adviser to the Kurdish-led administration running much of north and east Syria after eight years of civil war that has largely abated over the past year.

“But if these regional and international efforts are exhausted, then we will be in a total, grave military confrontation.”

Ankara views the Kurdish YPG militia, which spearheads the Syrian Democratic Forces, as terrorists posing a threat along its border. It has already sent troops into northern Syria twice in recent years targeting the Kurdish fighters.

Turkish President Recep Tayyip Erdogan had said on Sunday that a military operation was imminent in Syria east of the Euphrates river, territory which the SDF control and where U.S. forces are stationed.

Washington, which armed the SDF in the fight against Islamic State, had resisted Turkey’s demands for full control of a long strip of land that would extend 32 km (20 miles) into Syria.

Jia Kurd said a Turkish assault would lead to a “catastrophic conflict” that officials in the SDF region were doing all they could to prevent through talks with foreign states. But he added there was silence from European countries and “lack of seriousness” from Russia.

“On the American side, there are attempts to block the Turkish attack but it needs resolve.”

He repeated warnings from Kurdish leaders in recent months that an assault would create chaos that Islamist militants could exploit for a resurgence.

U.S. Defense Secretary Mark Esper said this week any Turkish operation into northern Syria would be “unacceptable.” He said the United States did not have any “ambition” to abandon the SDF, but stopped short of guaranteeing that it would protect them in case of a Turkish attack.

Aldar Xelil, the senior Kurdish politician, said he did not expect Washington and its allies to back away from helping the SDF combat Islamic State sleeper cells to secure the region.

The Turkish “threats are serious and have dangerous implications on Syria,” he added. “We do not want a war with any side. But if we come under any attack, we will not sit back and watch.”