The United States has started the "deliberate withdrawal" process of its forces from Syria, US military officials confirmed on Friday, but they refused to provide any details on exactly what troops and equipment were being moved.
"Out of concern for operational security, we will not discuss specific timelines, locations or troop movements," military spokesman Sean Ryan said in a statement.
A Defense Department spokesperson later said that while equipment was being moved out of Syria, troops were not withdrawing.
Separately, the head of the UK-based Syrian Observatory for Human Rights, Rami Abdel Rahman, confirmed that the US had started withdrawing troops from the airfield base near the town of Rmeilan in northeast Syria on Thursday evening.
Some 150 soldiers and 10 armored vehicles, along with some trucks and heavy equipment, left the town and crossed the Iraqi border, he said.
"This is the first such pullout of American forces" since the US President Donald Trump announced that American forces would leave Syria, Rahman said.
Kurds fear a Turkish offensive
Trump's decision to withdraw all of the 2,000 US troops from the war-torn country prompted shockwaves among US senior officials and US allies in December. US Defense Secretary James Mattis resigned soon after the announcement.
Opponents of the move claim that the pullout will allow Russia, Iran and the Syrian regime to expand their influence in the region. Many are also worried that the Kurdish forces, which spearheaded the fight against the "Islamic State" militants with US backing, would be left vulnerable to an imminent attack by Turkey.
Turkey regards the Kurd-dominated YPG units as an offshoot of the Kurdistan Workers' Party or PKK, which Ankara considers a terrorist organization. Turkish military has previously entered Syria in an apparent effort to drive Kurdish forces away from Turkey's borders.
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."
Earlier this week, however, US national security adviser John Bolton said the US would expect guarantees that the Kurds would be protected after American troops leave the area. The comments drew a rebuke from Erdogan, who slammed them as a "serious mistake."
Read more: Trump adviser John Bolton to leave Turkey without meeting Erdogan
On Friday, Bolton said that the militaries of the US and Turkey are set to continue negotiating on the Kurdish issue.
Washington was pursuing "assurances and protocols and procedures so that everybody feels comfortable with how this is going to happen," Bolton said in a radio interview with American reporter Hugh Hewitt.
"And we're hoping those discussions, which will continue next week, will produce results that are acceptable on both sides."