After capturing the Syrian city of al-Bab from ISIS, Turkish officials made it clear that the next military target was the city of Manbij, along the Euphrates River. Manbij was captured last year from ISIS by the Kurdish YPG, with considerable US military support.

Turkey had long insisted that Kurds aren’t allowed west of the river, where Manbij is, and the Obama Administration had assured Turkey that the Kurds would eventually withdraw from the city. They never did, and a deal between Syria and the YPG to cede nearby villages to the Syrian military aimed to block Turkish forces from advancing on the city. Now, US troops are joining in.

Pentagon officials say that a “small number” of US forces are being deployed to Manbij as “a visible sign of deterrence” aimed at preventing Turkey and the Kurds from fighting one another. Turkey hasn’t responded to the news, but is likely to be furious, as the deployment is inside Kurdish territory, and blocking their planned invasion.

The US has long faced the problem of being closely allied to the YPG in Syria, while Turkey, a NATO member, openly declares them a terrorist organization, and promises military attacks on them. The US seems to believe that direct deployments putting them in the way of the fighting would help, but it remains to be seen whether this will actually prevent Turkey’s attacks, or just shift them to different Kurdish territory.