Turkey's military incursion against Kurdish groups in Afrin, Syria, has helped bring US-backed ground offensives targeting ISIS to a near halt, multiple US officials tell CNN, putting the military campaign against the terror group at risk, an effort seen as one of the Trump administration's principle successes.
An official from the US-led coalition fighting ISIS told CNN that a small number of Kurdish members of the US-backed Syrian Democratic Forces had left the campaign against ISIS in Syria's Middle Euphrates River Valley, opting to join other Kurdish forces in Afrin as they battle Turkish troops and their local Syrian allies.
Although the contingent of the US-backed force fighting ISIS in that area is 80% Arab and 20% Kurdish, much of its leadership is ethnically Kurd.
The coalition official told CNN that those that have left for Afrin included some of the force's Kurdish commanders, limiting America's local allies' ability to conduct offensive operations against ISIS' few remaining territorial strongholds.
He said that the Kurdish fighters did not take any of the coalition provided weapons and equipment that had been given to them to help fight ISIS.
The Trump administration's decision to provide such weapons and equipment to Kurdish elements of the Syrian Democratic Forces was heavily criticized by Turkey, who sees such Kurdish groups as linked to the PKK, a separatist group that has waged a decade's long insurgency against the Turkish government.
Turkey launched an operation targeting Kurdish groups in Afrin in January, shortly after the US coalition announced plans to work with elements of the Syrian Democratic Forces to help stabilize areas of Syria that had been captured from ISIS.
While US officials noted that the US-led coalition continues to target ISIS with airstrikes, the halting of most ground offensive operations against ISIS risks undermining the recent gains against ISIS in the area, jeopardizing one of the Trump administration's biggest successes.
"We are aware of the departure of some Syrian Democratic Forces from the Middle Euphrates River Valley and continue to point out the potential costs of any distraction from the defeat-ISIS fight," Pentagon spokesman Eric Pahon told CNN.
"The Syrian Democratic Forces accepted coalition support with the guarantee they would not use it against Turkey or any other Coalition ally. The Syrian Democratic Forces leadership recently reaffirmed this commitment," Pahon added.
State Department Spokeswoman Heather Nauert encouraged Turkey to read the UN Security Council cease fire resolution on Syria, saying the document is clear in naming which groups are exempt.
Turkish government officials have said they will continue to go after Kurdish fighters in Afrin despite the resolution.
The commander of US Central Command, which oversees US military operations in the region, Gen. Joseph Votel, told Congress Tuesday that the Syrian Democratic Forces were "the most effective force on the ground in Syria against ISIS."
And while Votel acknowledged Turkey's "significant concerns along their border with longstanding PKK interests," he expressed concerns that the Turkish military's "activity in Afrin is detracting from our efforts against ISIS."