Turkey urged the United States on Thursday to halt its support for Kurdish YPG fighters or risk confronting Turkish forces on the ground in Syria, some of Ankara's strongest comments yet about a potential clash with its NATO ally.

The remarks, from the spokesman for President Recep Tayyip Erdogan's government, underscore the growing bilateral tensions, six days after Turkey launched its air and ground operation, "Olive Branch," in Syria's northwestern Afrin region.

In Washington, the Pentagon said that it carefully tracked weapons provided to the YPG and would continue discussions with Turkey.