The move comes even as relations between Washington and Ankara have soured in recent months over a number of issues, including Turkey's potential purchase of a Russian air-defense system.

Manbij, once in the hands of the Islamic State group, is now held by a US-backed alliance dominated by the Kurdish People's Protection Units (YPG).

Ankara considers the YPG "terrorists" and had previously threatened to attack the city.

US support for the YPG has strained relations with Turkey, which fears the emergence of an autonomous Kurdish region on its southern border.

Under an agreement with the United States to reduce tensions, Turkey started military patrols around Manbij in June, while the US conducted its own patrols.

Now troops from both countries are training together in Turkey to conduct joint patrols, US Army spokesman Colonel Sean Ryan said.

"Right now, they are still operating independent, coordinated patrols but they are also starting... the joint training," Ryan told Pentagon reporters. He did not say when the joint patrols would begin.

The Turkish and US troops are studying communications, rules of engagement and are undergoing medical training.

Fueling tensions, Turkey is embroiled in a dispute with Washington over the detention of a US pastor, and is in talks with Russia to buy the S-400 missile system.

President Donald Trump in August signed a defense authorization act that prohibits the delivery of F-35 stealth aircraft to Turkey if it goes ahead with the S-400 purchase.