Turkey's ground assault against an American-backed Kurdish militia in northern Syria threatens a further deterioration in relations with the United States, a key NATO partner, according to several regional experts.
President Tayyip Erdogan warned Wednesday that Turkey would expand its military offensive to the Syrian town of Manbij, where the Pentagon maintains Special Operations troops who are partnered with Kurdish forces that dominate the city.
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The Turkish offensive, now in its fifth day in the Kurdish-led Afrin enclave, seeks to oust from the area the U.S.-allied People's Protection Units, or YPG, which Ankara regards as an element of a militant Kurdish group that has pursued a decades-long insurgency in Turkey. Both the United States and Turkey consider the group, called the PKK, a terrorist organization.
"There is a real risk that the United States and Turkey could come to blows in Syria," said Nick Heras, a Middle East security fellow at the Center for a New American Security. "The United States wants to have its cake and to eat it too. It wants to continue to work with Syrian Kurds in eastern Syria as a core part of building stability post-ISIS, but it also wants to keep Turkey as a close NATO ally and it's become increasingly difficult for the United States to do both."
The Trump administration has responded tepidly to Erdogan's assault, acknowledging the "legitimate concerns" of terrorists crossing into Turkey from Syria while calling for restraint in the scope and duration of its military operations.
Turkish government officials have said their goal is to establish a 20-mile buffer zone across its southern border with Syria, where the YPG controls large swaths of territory. Turkey's prime minister estimates there are 8,000 to 10,000 YPG fighters in Afrin.
Elizabeth Teoman, a research assistant on Turkey at the Institute for the Study of War, said an escalation in the Turkish-Kurdish conflict threatens U.S. troops in both Syria and Turkey, where the Pentagon maintains two military bases. She said it will be key for the Trump administration to engage Turkish officials ahead of any potential follow-on operations in Manbij.
President Donald Trump is expected to have urged Turkey to de-escalate operations in a phone call with Erdogan on Wednesday, according to Reuters.
U.S. support for the Kurdish militia has long angered authorities in Ankara, who have repeatedly called on Washington to sever ties with its crucial anti-ISIS partner.
Erdogan last week accused the Trump administration of breaking a reported promise to cease support of Kurdish fighters upon the defeat of ISIS, after the U.S.-led coalition announced it would continue working with the Kurdish-led Syrian Democratic Forces on stabilization missions. The YPG makes up the backbone of the SDF.
"This is clearly one of the complications that is going to arise as the U.S. extends its military presence in Syria beyond the end of ISIS," said Bulent Aliriza, the director of the Turkey Project at the Center for Strategic and International Studies. "There is no way on earth there will not be initial tensions between Turkey and the United States if Turkey is to intervene against other areas without a willingness on the part of the U.S. to withdraw those forces, and Washington has given no indication whatsoever that it will do so."
Aliriza said if Turkey follows through with plans to move its military into Manbij it risks "major escalation" with the United States.
Turkey reportedly secured approval for the operation from Russia, which controls the airspace over Afrin. Russia withdrew troops from Afrin on Saturday after Turkish officials briefed Moscow on its plans, according to the Associated Press. Russia denied it okayed the assault.
The offensive underscores America's limited leverage in Syria given its engagement has been largely focused on the defeat of ISIS, according to Heras of the Center for a New American Security.
"President Erdogan is trying to make a statement that it is Erdogan and not Trump who will determine the future course of U.S. policy in Syria," he said. "Early on, Trump needs to do what Obama didn't do, which is to standup in Syria and say, ‘No, this is where the U.S. put its foot down.'"