The video below succinctly outlines Turkey's position on the connections between the PKK and the YPG, which the United States disputes.

The Turkish government sees the Kurdish factions in Syria as an extension of a domestic terrorist group, the Kurdistan Workers' Party, better known by its Kurdish acronym PKK. Though the United States has also formally designated the PKK as terrorists, it insists the Kurds it is working with in Syria against ISIS, known as the People's Protection Units or YPG, are separate and distinct.

Between August 2016 and March 2017, Turkey had conducted its own unilateral operation against various Kurdish groups northern Syria, called Operation Euphrates Shield . After that ended, the country continued to support the TFSA as a hedge against the Kurds making further gains.

U.S. officials have not named the specific group they faced off against, though they have made it clear they understand it was one from a loose coalition of ethnic Arab and Turkmen organizations that Turkish authorities are working with in Syria sometimes referred to as the Turkish-backed Free Syrian Army (TFSA).

“Our forces did receive fire and return fire and then moved to a secure location,” U.S. Army Colonel Ryan Dillion, the top spokesman for the U.S.-led task force fighting ISIS in Iraq and Syria, told the The Telegraph . “We have told Turkey it is not acceptable.”

The firefight involving American troops occurred near the contested city of Manbij in Syria, which has been a focal point for simmering tensions between United States and Turkish-supported factions since March 2017 . This was the first time U.S. personnel had been directly involved in a clash, though, and thankfully no one was injured on either side.

U.S. forces in northern Syria have exchanged fire with Turkish-backed rebels for the first time ever as the situation in the country continues to become ever more complex. To the west, Russian troops have moved into another area along the Syrian-Turkish border, cutting a deal with Kurdish fighters and effectively blocking both Turkish and American forces from entering the area, while exposing possible rifts between the United States and the groups it supports in the region.

We at The War Zone have written at length in the past about how these complicated and often shifting allegiances, combined with the lack of clarity over America’s role in Syria after the defeat of ISIS – whatever that looks like – have increased the chances of U.S. troops and their partners ending up in a risky situation. With American special operators acting as de facto peacekeepers for months, this firefight near Manbij has seemed almost inevitable. “Coalition troops will continue performing patrols within the Manbij Military Council area of control,” Eric Pahon, a Pentagon spokesman, told CNN after the incident with the Turkish-support rebels. “Coalition forces are there to monitor, deter hostilities and ensure all parties remain focused on our common enemy and the greatest threat to regional and world security, ISIS.” Keeping the focus on ISIS is important for the United States, which has special operations forces closely assisting the American-backed Syrian Democratic Forces (SDF) as they work to secure the city of Raqqa, which has been the terrorist group’s de facto capital. The SDF predominantly consists of element of the YPG, along with a smaller number of Arab fighters.

Morukc Umnaber/picture-alliance/dpa/AP Images SDF fighters take cover in a building in Raqqa.

The fighting in Raqqa has been hard going and any diversion of effort or dangerous infighting might slow the offensive down even further. In July 2017, the Trump Administration ended support for certain Arab members of the so-called Vetted Syrian Opposition (VSO), a separate U.S. supported coalition, who had refused to stop battling the brutal regime of Syrian dictator Bashar Al Assad and refocus on ISIS. Earlier in August 2017, Jaish al Thuwar, a Kurdish faction aligned with the YPG and the SDF, reportedly fired a U.S.-supplied TOW anti-tank missile at Turkish-backed rebels as part of ongoing skirmishes. In that instance, the U.S. military said that while the Kurdish group was known to have connections with the SDF, it was not an American-supported group itself. The United States also trying to distance itself from these breakaway Kurdish elements. In line with keeping things laser focused on crushing ISIS, earlier in August 2017, the United States said it would establish a shared ceasefire monitoring center with Russian and Jordanian personnel in Jordan's capital Amman. The U.S. government had previously brokered a deal with the Kremlin, along with Jordan and Israel, to establish a safe zone of sorts in southern Syria.

Ismail Coskun, IHA via AP Turkish troops head toward the Syrian border in an armored vehicle in 2016.