US Defense Secretary Mark Esper said on Tuesday any Turkish operation into northern Syria would be “unacceptable” and Washington would prevent unilateral incursions, Reuters reports.

President Recep Tayyip Erdogan said on Sunday that Turkey, which already has a foothold in northwest Syria, will carry out a military operation in a Kurdish-controlled area east of the Euphrates in northern Syria.

“Clearly we believe any unilateral action by [Turkey] would be unacceptable,” Esper told reporters in Tokyo. “What we’re going to do is prevent unilateral incursions that would upset, again, these mutual interests… the US, Turkey and [the Syrian Democratic Forces] share with regard to northern Syria,” Esper said.

The SDF, which includes the Kurdish YPG militia, have taken control over the last four years of much of northeastern Syria from Islamic State (IS, formerly ISIS) militants. Ankara sees the YPG as a terrorist organization.

Tags: ; ;