The U.S. and Russian Federation moved this week to block a threatened drive by Turkey to seize Manbij, a town in northern Syria about 40 kilometers (25 miles) from the Turkish border. Turkish President Recep Tayyip Erdogan comes to Moscow on Thursday with his defense minister for talks with Putin.
The definition of "terrorist" has become a contentious one during the six-year Syrian civil war, with Bashar al-Assad's government and its supporters using the term to describe all opposition groups, including those supported by Turkey and the US-led coalition.
Turkish Prime Minister Binali Yildirim says the United States risks major damage to its relationship with North Atlantic Treaty Organisation ally Turkey if Kurdish forces are included in the fight to retake Raqqa, the Islamic State group's de facto capital. In Manbij, "the U.S.is raising a flag, Russian Federation is raising a flag nearby, things have turned into a flag competition", Yildirim said in an interview with ATV television late Monday.
Speaking in Ankara, Yildirim said Syria needed to be rid of "all terrorist groups" including Al-Nusra, Syrian Kurdish militia as well as IS jihadists. President Tayyip Erdoğan and other Turkish officials have been saying for a long time that if the USA would abandon cooperation with the YPG, then Turkey and the Syrian Arab rebels who are supported by Turkey would fully cooperate to take the key Syrian city of Raqqa from ISIL. "If this coordination is not secured, the risk of conflict that is most undesirable may arise", Yildirim warned.
Although Russia, Turkey and the U.S. are fighting on the same side, there are doubts and tensions that remain over the involvement of Kurdish militia forces. Ankara launched a military offensive into Syria in August past year to push the IS away from its border and prevent the emergence of a Kurdish corridor.
The advance is part of a dayslong government offensive against IS backed by Russian airstrikes. Turkey has long insisted that unless the Syrian Kurds pull out of the town it will take matters into its own hands.
Turkey and the US are locked in a heated dispute about USA plans to liberate Raqqa, with Turkey insisting its own military and allied forces in Syria should mount the fight and that USA -backed Syrian Kurds should be excluded. The U.S. would continue to designate the PKK as terrorists, despite knowing the organic links in between, but would not call the YPG as terrorists.
Syrian regime forces and their Russian partners represent an additional layer of complexity.
The fight against Isis has made the groups uncomfortable allies but the so-called Islamic State's impending defeat in northern Syria is letting former divisions escalate into open conflict along new frontlines.
Turkey had often said that the next target of its cross-border Syria campaign would be the flashpoint town of Manbij, which is now controlled by the US-backed Syrian Democratic Forces, a group dominated by Kurdish fighters.
Asked whether this is a new mission for USA troops in Syria, Davis said, "It is, absolutely".
Full-scale hostilities between the Turks and Kurds would deal a major setback to efforts to capture Raqqa, according to Joshua Landis, head of the Center for Middle East Studies at the University of Oklahoma.
In January, the SDF was provided by the US with armored vehicles for the first time ahead of the planned Raqqa offensive. The Pentagon has described their mission as one to "reassure and deter" local parties from attacking one another, a new role for the US military in the Islamic State war, and one that could set a trend for the remaining cities to be conquered. U.S. Special Operations troops have now trained thousands of Arab recruits, who are expected to be put on the front lines of the eventual battle for Raqqa.
". It appears that the US may carry out this operation with the YPG, not with Turkey".