There are United States forces in the Sunni Arab-majority Manbij - which lies just 30 kilometres south of the Turkish border - and Washington has been closely working with the YPG in the fight against IS.
The offensive did not come as a surprise as Turkish President Recep Tayyip Erdogan had made several warnings since mid-September about impending full-blown military action against the YPG positions on the east of the Euphrates.
"The joint patrol in Manbij between Turkish armed forces and the U.S. began today at 3.53pm", Defence Minister Hulusi Akar told lawmakers, according to state-run news agency Anadolu.
However, even as the joint patrols were due to begin this week, Turkey announced a new offensive against the Kurds on the opposite bank of the river, into territory where the SDF has USA troop support. Turkey launched the operation in 2016 and ended in 2017 to drive away Islamic State (IS, formerly ISIS) militants and the Syrian Kurdish YPG militia from its border with Syria.
The Turkish military said in a statement on Wednesday that a border command post in Sanliurfa province came under "harassment fire" from Kurdish "terrorist organization" forces, resulting in one military vehicle being destroyed.
President Recep Tayyip Erdogan has vowed to crush separatist Kurdish militants operating in Syria along his country's border, seeing them as an extension of the separatist Kurdish PKK group classified as a terrorist organization by Turkey, the US and the European Union.
Both the European Union and the US classify the PKK as a terrorist organization, but they differentiate between the PKK and other Kurdish groups.
Turkish and US troops on Thursday began jointly patrolling areas around the northern Syrian town of Manbij, part of a roadmap for easing tensions between the two North Atlantic Treaty Organisation allies, Turkey's defense minister announced.
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A U.S. base near Manbij, Syria. Conducting joint patrols is seen as a way to tamp down potential violence between the various groups in the area.
In a speech to the Turkish parliament on Tuesday, President Erdogan said that the latest attacks marked the beginning of "more extensive and effective operations" against YPG positions east of the Euphrates.
"After Manbij, our next venue will be east of the Euphrates", Akar pointed out.
"Planning and preparations for this have already been completed".
To ease ties, the countries agreed to a road map in June that included the YPG withdrawing from Manbij and establishing the joint patrols in the city.
Past offensives halted at the banks of the river, in part to avoid direct confrontation with the US.
However, Ankara rejects these accusations and claims the deal is being implemented as planned to create a demilitarized buffer zone around the opposition-held Idlib region, the last stronghold of the anti-Assad insurgency.