PARIS/WASHINGTON — After the United States delivered an ultimatum for their exit, fighters linked to Syria’s Kurdish-led Syrian Democratic Forces withdrew from the northern border city of Manbij and headed east across the Euphrates River, after handing the city over to predominantly Sunni Arab rebels of the Syrian National Army, Al-Monitor has learned. 

A US official told the SDF on Monday that they had to withdraw from their positions west of the Euphrates River, and that the Pentagon would not provide any protection for them if they did not comply, the sources speaking not for attribution told Al-Monitor. 

The ultimatum came as the militants failed to comply with an agreement brokered by the United States to pull out of the city in exchange for assurances that Turkey and its SNA allies would not attack the SDF east of the river. As the militants dug in, SNA groups backed by Turkish airpower encircled Manbij and finally breached the strategic Qara Qwzaq Bridge linking both sides of the river and began advancing toward the border town of Kobani amid heavy clashes.  

The Kurdish militants’ obduracy exasperated administration officials as they parleyed with Ankara to limit its offensive, which has triggered panic and upheaval across the Kurdish-led northeast of the country.