Any Turkish incursion into Syria "unacceptable," will prevent it: Pentagon chief

U.S. Defense Secretary Mark Esper said on Tuesday that any Turkish operation into northern Syria would be "unacceptable" and the United States will prevent unilateral incursions, as tensions between Washington and Ankara simmer.

"Clearly we believe any unilateral action by them (Turkey) would be unacceptable," Esper told reporters travelling with him to Japan.

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