Any Turkish Invasion Into Syria “Unacceptable”: Esper

US Defense Secretary Mark Esper said on Tuesday that any Turkish invasion into Syria would be “unacceptable”.

In press statements, on the sidelines of his current visit to Japan, Esper added that US will prevent any unilateral incursion by Turkey into northern Syria.

"What we're going to do is prevent unilateral incursions that would upset, again, these mutual interests that the United States, Turkey and the SDF share with regard to northern Syria," Esper said.

A team from the Pentagon was in Turkey to speak with Turkish officials about the issue and Esper said he was hopeful that an agreement could be reached with Ankara.

Esper suggested that a Turkish operation into northern Syria could affect the SDF’s focus on ensuring Islamic State did not retake the territory it once held in Syria and the ability of the US-backed forces to hold the thousands of alleged Islamic State fighters in detention.

Noteworthy, the SDF stands for the Syrian Democratic Forces. With US backing, the SDF, which includes the Kurdish YPG militia, have taken control over the last four years of much of northeastern Syria from Daesh militants. Ankara sees the YPG as a terrorist organization.

Ties between the two NATO allies have been strained over a host of issues, including the United States’ removal of Turkey from the F-35 fighter jet program after Ankara bought and took delivery of Russian S-400 missile defenses that Washington sees as a threat.