Secretary of State Rex Tillerson on Monday called on Turkey to show restraint as its forces attacked U.S.-backed militias in northern Syria for a third day, the latest strain in relations between Washington and Ankara, a NATO ally.
Tillerson, speaking in London, acknowledged Turkey's "legitimate security concerns" because President Recep Tayyip Erdogan's government views the Kurdish-dominated militias as terrorists and insurgents seeking an independent state.
Tillerson urged Turkey to work with Washington to focus on fighting Islamic State and "securing a peaceful, stable...and unified Syria" through negotiation. He described the largely Kurdish Syrian Democratic Forces as a multi-ethnic group.
Using airstrikes and ground troops, Turkey has sought to clear the Afrin area of northern Syria of Kurdish fighters, and has vowed to move on to the Manbij region about 90 miles east, which was once an Islamic State stronghold.
The United Nations Security Council scheduled an emergency meeting later Monday to debate ways to stop the Turkish offensive and protect civilians.
In November, President Trump said the U.S. would wind down its arming of Kurdish fighters in Syria, apparently hoping to appease Erdogan.
But in recent weeks, the U.S. military announced plans to train and arm a 30,000-member "multi-ethnic" security force along Syria's northern border with Turkey, which Ankara immediately saw as a front for the Kurds. Tillerson later backed away from that plan.
The U.S.-backed Kurdish militias have helped lead the ground war against Islamic State in Syria, complicating the murky alignment of forces in a conflict that has claimed hundreds of thousands of lives in the last seven years.