The US and Turkey on Sunday began joint patrols in northeastern Syria aimed at easing tensions between Ankara and US-backed Kurdish forces. 

Six Turkish armored vehicles crossed the border to join US troops in Syria for their first joint patrol under a deal reached between Washington and Ankara, an AFP journalist reported.

Two helicopters overflew the area as the Turkish vehicles drove through an opening in the concrete wall erected between the two countries.

The agreement reached on August 7 aims to establish a "safe zone" between the Turkish border and the Syrian areas east of the Euphrates river controlled by the Kurdish People's Protection Units militia.

The YPG is an ally of the US but seen as a terrorist organization by Turkey.

Turkish President Recep Tayyip Erdogan has threatened to launch an operation against the YPG in Syria unless progress is made on setting up the safe zone.

Erdogan said his US counterpart Donald Trump had promised it would be 32 kilometers wide.

A joint center of operations was recently established as part of the agreement. 

Turkey previously conducted cross-border operations in northern Syria supporting Syrian rebels in 2016 against IS and in early 2018 against the YPG.

Ankara says the YPG militia is a "terrorist" offshoot of the outlawed Kurdistan Workers' Party.

The PKK, which has waged an insurgency against the Turkish state since 1984, is blacklisted as a terrorist group by Ankara, the US and the European Union.