Turkey strongly opposes the involvement of Syrian Kurdish forces in the operation.
The Pentagon said Monday that USA forces have also taken up positions on the outskirts of Manbij to try to keep a lid on tensions.
The U.S. military has carved out a new role in Syria, with small numbers of troops now positioned to prevent an escalation of violence among an array of militias and other forces that have converged on an increasingly complex battlefield.
Turkey is home to some 3 million " mostly Syrian " refugees, and is also a main point for the delivery of aid to Syria. But the top American commander for the fight against IS has said he's seen "zero evidence" the YPG has posed a recent threat to Turkey.
Turkish President Recep Tayyip Erdogan, addressing a campaign rally in the Turkish capital Ankara, reiterated his readiness to confront the Kurdish forces.
Since 2012, Mercy Corps has conducted from Turkey one of the largest humanitarian operations in Syria, delivering urgently needed, lifesaving assistance to 350,000 to 500,000 innocent civilians in Syria each month.
The meeting of the top brass came ahead of a visit by Turkish President Recep Tayyip Erdogan to Russian Federation.
Turkey sent troops across the border into Syria in August, backing Free Syrian Army rebels in battles against Islamic State.
"There is a need for an effective coordination in the efforts to clear Syria of all terror groups because so many countries are involved there", he told reporters.
Although Turkey has spent years trying to unseat the regime of Bashar Al Assad by funnelling arms to rebel groups, Ankara and its proxies have avoided combat with government forces since the Turkish military intervention last year, focusing on the pursuit of ISIL and the YPG.
Hands-on with the new Nintendo Switch and 'Zelda: Breath of the Wild'
Zelda: Breath of the Wild was supposed to be Wii U's saving grace but the console's fall from it was simply irredeemable. I think it's a little bit weird that Link still can't talk, but I understand Nintendo's decision to give Zelda a voice.
A replay of US and Soviet troops meeting on the Elbe?
Manbij lies about 30 kilometers to the west of the Euphrates River and is strategically important to unite the two Kurdish cantons in northeastern Syria with the third Afrin canton in the western part of the river.
"The Turkish military is present in Syria and carries out military operations there, and the Russian military continues activities to support the Syrian armed forces - this requires very close interaction and coordination", the Kremlin spokesman said.
Kurdish and Arab Syrians, backed by the US -led coalition, retook Manbij from the Islamic State in Iraq and Syria (ISIS) past year. The rising tensions between the Kurds and the Turks comes as the United States considers how best to retake Raqqa from ISIS, including to what extent the Kurds and Turkey should participate.
"Statements by Turkish officials about ownership of Syrian territory by this or that group in Syria are unprecedented and undermine Syria's territorial integrity and must therefore be stopped", remarked Logoglu.
Asked whether this is a new mission for USA troops in Syria, Davis said, "It is, absolutely".
Oh, and there are Russian, U.S., Syrian and Turkish jets flying around throughout all of this.
USA military leaders have given their recommendations on the fight against ISIS to the White House.
Mercy Corps said it would go ahead with its ground operations in Syria, and "our priority right now is to limit any adverse effects our departure from Turkey may have on the innocent men, women and children who depend on our assistance". The Russians have not remained idle either.
And as a Turkish official admitted to Reuters, the United States is committed to conducting Raqqa with the SDF, not Turkey.