Sunday's military deployment could mark a rapid change in the dynamics between the two countries after Trump announced American forces would quit Syria following a December 14 phone call with his Turkish counterpart Recep Tayyip Erdogan.
US troops are preparing for withdrawal following Washington's surprise decision to pull out of Syria, where it has backed the Syrian Kurdish YPG forces against Islamic State.
Trump in two tweets claimed Turkey's Erdogan would "eradicate whatever is left" of the jihadist group Islamic State (IS) in Syria, targeted in a four-year multinational campaign and spearheaded inside northeastern Syria by Kurdish fighters backed by 2,000 U.S. troops.
The move gives Turkey more scope to target US-backed Kurdish fighters who have led the ground battle in the war against IS but whom Ankara sees as terrorists.
Five days after the call with Erdogan, Trump announced in a tweet that he was removing the troops, claiming: "We have defeated ISIS in Syria, my only reason for being there during the Trump Presidency".
The two leaders reportedly agree to coordinate to prevent an authority vacuum from developing as the withdrawal process begins.
Erdogan said, "I hope that our meeting will be beneficial for our countries and our region".
In the past two years, Turkey has conducted two offensives into northern Syria, dubbed "Euphrates Shield" and "Olive Branch".More news: Pochettino bookmakers' hot favourite to take over at United
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"My views on treating allies with respect and also being clear-eyed about both malign actors and strategic competitors are strongly held and informed by over four decades´ immersion in these issues", Mattis wrote to Trump, who has sought closer ties with Russian Federation and heaped contempt on North Atlantic Treaty Organisation and other alliances.
Trump, in a late night tweet on Sunday, said he dialled Erdogan and had a productive session of talks.
Until Trump's announcement this week on Twitter, administration officials were talking about an extended stay in Syria, pointing to a remaining IS pocket with thousands of fighters, and also expressing a desire to counter Iran and restrain Russian Federation.
"An ally should be dependable", Macron said at a press conference during his visit to Chad. "The SDF is fighting against the terrorism that fomented attacks against Paris and elsewhere".
Turkey is massing troops near a town in northern Syria held by a Kurdish-led force backed by the United States, a war monitor and Turkish media have said.
Turkey views the Kurdish fighters as terrorists due to their links to a Kurdish insurgent group inside Turkey.
The Turkish president also wished a happy new year to the U.S. president and American people.
"We have beaten them and we have beaten them badly", Trump said Wednesday in a video post on Twitter.
The resignation of outgoing Defense Secretary James Mattis, and his letter explaining his reasons, will leave a "mark on the president", former GOP Rep. Mike Rogers said Monday, while appearing on CNN with retired NATO Supreme Allied Commander Wesley Clark.