"CJTF-OIR has begun the process of our deliberate withdrawal from Syria", spokesman Colonel Sean Ryan told the AFP news agency in a statement, referring to the US-led anti-Islamic State group (IS) force.
The U.S. military said Friday it has begun withdrawing troops from Syria, initiating a drawdown that has blindsided allies and sparked a scramble for control of the areas that American troops will leave.
Giving a subsequent speech about broader US policy in the Middle East at the American University in Cairo, Pompeo said "now is the time" to bring America's forces out of Syria.
About 10 armored vehicles in addition to some engineering machines pulled out of Rmeilan, Syria, Thursday night headed for Iraq, according to the Syrian Observatory for Human Rights, which monitors the Syrian conflict.
Trump has said he agreed to submit areas under the control of Kurdish militants to Turkey, prompting outrage among the community in northern Syria and warnings by U.S. politicians that Washington was betraying its allies in the region.
The move fueled questions about the USA commitment to eliminate remaining pockets of Islamic State militants as well as the fate of Kurdish forces that have fought alongside the US but that Turkey considers terrorists.More news: Congo says Felix Tshisekedi wins presidential poll
Earlier this week, the US national security adviser John Bolton said American troops will not leave northeastern Syria until IS is defeated and American-allied Kurdish fighters are protected, signaling a slowdown in Trump's initial order for a rapid withdrawal.
The statement coming a day after U.S. Secretary of State Mike Pompeo in Cairo defended the withdrawal, insisting it was not a retreat. The U.S. has about 2,000 troops in the country.
The U.S. has about 5,200 troops in Iraq to assist its security forces, and Trump has given no indication he intends to withdraw them any time soon.
There are 2,000 USA troops in Syria and while the military has orders to follow the president's decision to withdraw, they have no timelines attached for how long it will take.
A senior Kurdish politician said the Kurds are aware of the USA beginning its withdraw process, describing it as "America's decision".
"The execute order for Syria has been signed", a United States military spokesperson told AFP when asked about the withdrawal order, without providing further details.More news: United States to leave troops in southern Syria as bulwark against Iran
Pompeo's remarks in Cairo also appeared to contradict Trump's announcement, drawing immediate criticism from Middle East experts as well as officials who served under former U.S. president Barack Obama.
Turkey's Defense Minister Hulusi Akar reviews an honor guard as he arrives for a meeting with the commanders of military units on Syrian border in Sanliurfa, southeastern Turkey, Jan. 11, 2019.
Uncertainty over the timing and terms of the Syria pullout have raised questions about the Trump administration's broader strategy for fighting Islamic extremism, including Trump's stated intention to reduce USA forces in Afghanistan this summer.
In Ankara on Tuesday, Erdogan refused to meet with U.S. National Security Adviser John Bolton, who earlier had appeared to set conditions on the U.S.withdrawal, including the lasting defeat of the Islamic State and guarantees that Turkey would not attack the YPG.
"When the time and place comes, the terrorists here will also be buried in the ditches and trenches they have dug", the minister said in southern Sanliurfa province.
"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. She said Russian Federation has not seen public statements laying out the US strategy in Syria and so can not be sure that the U.S.is serious about leaving.More news: Shannon Sharpe on why the Kliff Kingsbury hiring is a 'terrible' call