A US military spokesman said some special forces soldiers who had been deployed to support the Turkish forces have been withdrawn.
The US-led international coalition battling to defeat the Islamic State group is not backing a drive by Turkish forces and Syrian rebels to retake a jihadist stronghold in northern Syria, the Pentagon said Wednesday.
Their offensive on the city of Al-Bab is not being supported by coalition air strikes because it was "independently" launched by Turkey, said US Colonel John Dorrian, a spokesman for the coalition fighting the jihadist group in Syria and Iraq.
"That's a national decision that they have made," Dorrian said, speaking from Baghdad in a videoconference with reporters.
The US military spokesman said the United States had withdrawn some special forces soldiers who had been deployed to support the Turkish forces and their allies.
"They are not a part of the advance in Al-Bab," he said.
The lack of coalition support for the Al-Bab operation illustrates the strained ties as Turkey and its allies adopt disparate strategies for defeating IS in areas the jihadists still control in northern Syria.
"What we would like to do is to continue to work with them (the Turks) to develop a plan where everyone remains focused" on defeating IS, Dorrian said.
He warned against the partners "converging on a way that can be unhelpful."
Al-Bab, a city of 100,000 about 30 kilometers (20 miles) from the Turkish border, has been a key target for Turkey and its Syrian rebel allies since its campaign began on August 24.
Ankara launched its unprecedented cross-border operation saying it was targeting both IS and the Kurdish People's Protection Units (YPG) militia, which has been a key opponent of the jihadist group.
Against Turkey's wishes, the United States and its allies want to continue to count on the Syrian Democratic Forces (SDF), notably for its offensive against Raqa, another IS stronghold in northern Syria.
But Turkey suspects that the Kurdish-led SDF is only a smokescreen for the YPG, a group it brands a terrorist organization.