Ufuk Ulutas is the director of foreign policy studies for the SETA Foundation for Political, Economic and Social Research.

As long as the Y.P.G. seems more interested in expanding its control on the border with Turkey than in fighting ISIS, Turkey will clash with it. And if the United States were to stop arming the Y.P.G. in response to its attacks on Turkish and U.S. allies around Aleppo, the specter of its allying with Russia will be real.

Supporting forces linked to terrorism, like the Kurds in Syria, to fight another terrorist organization, ISIS, brings high risks.

There are already strong indications that it has been coordinating with Russian forces that are propping up the Assad regime. Its intertwined nature with the designated terrorist organization -- the P.K.K. -- and its demographic engineering in northern Syria as documented by Amnesty International and others, have added to Turkey’s fears.

In light of the latest terrorist attack in Ankara by a suicide bomber who entered Turkey from Y.P.G.-controlled territory, Turkey is left with no room to tolerate further Y.P.G. activity especially in areas where Turkey plans to create a terror-free zone. Turkey wants to clear a 90-kilometer strip of land, currently controlled mostly by ISIS and partly by the moderate opposition, to create a safe heaven for Syrian refugees. But the Y.P.G.'s latest attacks target dwindling moderate forces and complicates Turkey’s plans in that strip of land.

Nevertheless, there are still some steps to reduce tensions for which the United States could lay the groundwork.

The Y.P.G. should stop attacking the territory controlled by the moderate opposition and withdraw from the recently captured areas. The Y.P.G.’s aggression in northwest Syria not only forces Turkey to reciprocate but also harms the fight against ISIS by targeting anti-ISIS forces.

The United States should condition its support for the Y.P.G., as it has with the Syrian opposition, on its commitment to focus on ISIS. At the end of the day, militarily supporting a terrorist organization or, for the sake of argument, a terror-linked group such as the Y.P.G., to fight another terrorist organization, ISIS, brings high risks, and this is the gist of Turkey’s sensitivities that must be addressed by its NATO ally, the United States.

Turkey and the United States had reportedly agreed on the basics of an operation to clear remnants of ISIS out of the border areas to form a springboard to ISIS’s stronghold Raqqa. The two countries and others, like the Saudis, should start that operation immediately.

The long-term fight against ISIS and other terrorist groups requires more than what the Y.P.G. can offer, and must be done through an international coalition by addressing the conditions that nurture ISIS.



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