The US-led coalition and Turkey conducted their third joint patrol in north-east Syria on Friday, part of a plan designed to defuse tensions between Washington's two allies – Turkey and the Syrian Kurds.
The patrol followed a telephone call late on Thursday between Turkish Defense Minister Hulusi Akar and US Defence Secretary Mark Esper during which Mr Akar reiterated that Turkey wont' accept a delay in the creation of what it calls "a safe zone" and would act alone if necessary to set it up.
Mr Akar also told Mr Esper that Turkey would end the joint patrols "if there are distractions, delays" and urged the US to end its support to Syrian Kurdish fighters.
Ankara views Syrian Kurdish fighters as an extension of a Kurdish insurgency within Turkey and wants them away from the Turkey-Syria border. It has repeatedly threatened to carry out a military operation to push the Kurds away.
Turkey had carried out military incursions with allied Syrian groups in western Syria to drive out Kurdish fighters, as well as ISIS militants, and has stationed troops there.
But a Turkish military operation in northeastern Syria would carry a larger risk, bringing Turkish soldiers into a zone where at least 1,000 US troops are deployed.
Mr Akar told his US counterpart Turkey "would not allow the establishment of a terror corridor to its south," according to his statement.
The coalition said the patrol went ahead as planned and Turkey's defense ministry said it was in an area east of the town of Tal Abyad.
Washington says the deal reached with Ankara in August aims to address Turkey's security concerns.
So far, fighters from the most prominent Syrian Kurdish group – the People's Protection Units or YPG – have moved away from border posts.
But Turkey remains unhappy with the size of the area it calls a "safe zone." It also wants some of the 3.6 million Syrian refugees to return there.
Turkish President Recep Tayyip Erdogan told parliament that Turkey plans to settle 2 million refugees in the zone, and will hold a donors' conference to help build homes and infrastructure for them.
It is not clear how Turkey plans to move the largely Sunni Arab Syrians it is hosting from many parts of Syria into the Kurdish-dominated region, and whether the US is on board.