Turkish President Recep Tayyip Erdogan has repeatedly threatened to launch an attack on the city, near which U.S. troops are stationed as part of their support to a Kurdish-led alliance fighting Islamic State (IS), AFP reported.

Pro-Ankara Syrian rebels control territory to the north and west of the city held by the Kurdish-led Syrian Democratic Forces (SDF) alliance.

The rebels control Jarabulus near the Turkish border to the north, as well as Al-Bab to the west of Manbij.

"We're on high alert. There are always skirmishes at night," Kurdish fighter Shiyar Kobane said. "They fire mortar rounds and shell our positions."

Coalition forces carry out regular patrols on the frontline and "have increased their patrolling tours recently", SDF commander Khalil Mustafa told AFP.

Reporter’s code: 50101