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. He said the USA will not discuss a specific timeline, locations or troop movements out of concern for operational security.
In the past 24 hours, US forces have withdrawn 10 vehicles and 150 personnel from the Rmelan military base, one of the first installations the USA -led coalition established in Syria in 2014, according to the Syrian Observatory for Human Rights.
Some 150 soldiers and 10 armored vehicles, along with some trucks and heavy equipment, left the town and crossed the Iraqi border, he said.
There has been confusion over plans to implement Trump's pullout order amid threats from Turkey to attack the Kurdish fighters, who are seen by Ankara as terrorists due to their ties to insurgents within Turkey.
But following a backlash from Republicans and Democrats in Congress and the resignation of Defense Secretary Jim Mattis, Trump said the troops would be withdrawn "slowly".
Most recently, both the Pentagon and U.S. National Security Adviser John Bolton have said there is no deadline for U.S. troops in Syria to return home.
US Secretary of Defense Mike Pompeo stressed on Thursday that the alleged US withdrawal from Syria was not "a change of mission".
The amphibious assault ship USS Kearsarge, which had been moored in Crete, is leading a group of vessels towards the eastern Mediterranean to support the 2,000 United States troops as they leave the Kurdish-majority part of northeastern Syria, Pentagon officials told The Wall Street Journal.
A senior Kurdish politician says the Kurds are aware of the USA beginning to withdraw from Syria, describing it as "America's decision".
Turkish Foreign Minister Mevlut Cavusoglu said he will carry out the long-planned offensive against the YPG, regardless of the US withdrawal pace.
Very complicated: Bolduc, who served in the Pentagon during the USA troop withdrawal from Iraq in 2011, said the logistical challenge of getting out of Syria will be less taxing, but the Pentagon still must discern important questions - such as the size of the pullout, and the weapons and equipment that will be turned over.
The US-backed, Kurdish-led Syrian Democratic Forces (SDF) said the move had "dangerous implications" for stability, would "negatively affect the campaign against terrorism" and create "a political and military vacuum".
USA troops have been involved in the Syrian conflict since 2014.
"When the time and place comes, the terrorists here will also be buried in the ditches and trenches they have dug", he said. He spoke before the announcement on the USA withdrawal and did not address it.
The US has begun its operation to pull troops out of Syria, sending naval vessels and back-up forces to the region to assist with the withdrawal.
"We believe it is important that the territories that will be vacated after the Americans leave will come under the control of the Government of Syria", she added.