Trump made the decision to withdraw some 2,000 American troops from Syria last month, amid consultations with the Turkish military over their planned operations in Syria. Trump has asserted that the IS group in Syria is defeated, but others have said a continued USA military presence is necessary to prevent a resurgence of the group.
After announcing the pullout, Trump tweeted that Turkey's Recep Tayyip Erdogan "has very strongly informed me that he will eradicate whatever is left of (the Islamic State) in Syria", adding that the Turkish strongman was "a man who can do it".
His top diplomat Mike Pompeo is on a whirlwind regional tour aimed at reassuring allies amid rising tensions between the U.S. and Turkey over the fate of Washington's Syrian Kurdish allies in the fight against the Islamic State group.
Mr Pompeo said the withdrawal of USA troops from Syria was a "tactical change" but the mission to destroy Islamic State and counter Iran's influence remained the same. "We are confident we can achieve an outcome that achieves both of those".
The US decision has injected new uncertainty into the eight-year-long Syrian war and spurred a flurry of contacts over how a resulting security vacuum will be filled across a swathe of northern and eastern Syria where the US forces are stationed.
But the USA pullout risks leaving the Kurds at the mercy of Turkey, which views the fighters as terrorists.
Mr Bolton was on a visit to Ankara to seek guarantees over the Kurdish fighters, but President Erdogan declined to meet him.
After media reports suggesting the departure of USA forces had begun, the Pentagon later said no troops had yet withdrawn and stressed that the battle against ISIS was continuing as US-backed forces try to capture the group's last remaining pockets of territory in Syria.
US troops have been involved in the Syrian conflict since 2014.
Once the troops are gone, the US will have ended three years of organizing, arming, advising and providing air cover for Syrian, Kurdish and Arab fighters in an open-ended campaign devised by the Obama administration to deal ISIS a lasting defeat. "We will be like second-class citizens at best, if we survive as Syriac Christians and Kurds".
A female healthcare worker who was kidnapped by the PKK terrorist group in June 2013 and was taken to several places including Syria where she received medical education from foreigners revealed the terrible conditions women face in the terror group's camps after surrendering to Turkish security forces.
The YPG is an important ally in the USA war against the Islamic State.
Speaking on January 8, Bolton appeared to backtrack on the White House's position saying there was no timetable for the United States' drawdown in Syria. He described a "big and growing" coalition to exert pressure on Iran.
The U.S. has started "the process of our deliberate withdrawal from Syria", Col. Sean Ryan, a spokesman for the coalition fighting the Islamic State group, told the Associated Press without further elaboration.
The Defense Department wants to show progress to Trump and the public that they are following through on the President's orders to withdraw troops even though Bolton has indicated troops could remain for some time. It also led to major criticism that the USA was abandoning its local Kurdish allies amid Turkish threats of an imminent attack.
Media captionWas Trump right to say IS is beaten?