The US-led coalition says it is helping to create a thousands-strong “Border Security Force” in Syria using Kurdish SDF militias. Washington's support, branded “unacceptable” by Ankara, is further straining bilateral ties.

Some 230 new recruits are already undergoing training in the “BSF’s inaugural class,” the Coalition’s Public Affairs Officer Colonel Thomas F. Veale told the Defense Post. The border force will be stationed along Kurdish-controlled parts of the Syrian border with Iraq and Turkey, as well as along the Euphrates River valley. It is estimated to reach a total strength of 30,000, according to the official.

Around half of the new unit will be comprised of Syrian Democratic Forces (SDF) veterans, while the other half is being recruited. “The base of the new force is essentially a realignment of approximately 15,000 members of the SDF to a new mission in the Border Security Force as their actions against ISIS [Islamic State] draw to a close,” the Coalition’s Public Affairs Office told Reuters in an email.

The move prompted discontent from one of Washington’s key NATO allies – Turkey. The catch here is that battle-hardened Kurdish YPG units – part of the SDF – are viewed by Ankara as an extension of the “terrorist” Kurdistan Workers’ Party (PKK). Continuous US support for the YPG has put a major strain on relations between the two states.

“The US, providing support to the PKK’s Syrian branch, PYD-YPG, on the grounds of ‘fighting ISIS,’ is taking some worrying steps to legitimize this terrorist [group] and make it lasting in the region,” Turkish presidential spokesman Ibrahim Kalin said on Sunday, as quoted by NTV.

“It is absolutely not possible for this to be accepted.”

The new border force is expected to be based on the territorial principle, as its members will “serve in areas close to their homes” in order to ensure that “the ethnic composition of the force will be relative to the areas in which they serve.”

While Turkey has repeatedly voiced its displeasure at America’s support for the Syrian Kurdish militias, Washington is keen to reassure Ankara that its policy of arming the Kurds is “necessary to ensure a clear victory” in Syria’s Raqqa.

Following the capture of the key city from Islamic State militants, the US military announced plans to scale down its support for the YPG. The idea of relying in future on “local and police” forces was already considered by US Defense Secretary James Mattis back in December.