The White House has not clarified what the stay-behind mission will entail, nor how long it will last.
"To those groups who are betting on the Americans, we say the Americans will not protect you," Syrian President Bashar al-Assad said.
The move comes as Kurdish leader Ilham Ahmed's Syrian Democratic Council enters tough negotiations with the Syrian President Bashar al-Assad's government in hopes of finding peace.
The Syrian Democratic Forces claimed President Donald Trump's pullout from Syria was still in its "theoretical form" but they are already reportedly giving up positions in fear of a Turkish attack.
"Nothing can be achieved by threatening Turkey economically," said the country's foreign minister, Mevlut Cavusoglu, as the Trump administration warned Ankara against ordering an offensive against Kurdish forces.
Turkey has denied U.S. assurances of protection for Pentagon-backed Kurds in Syria, prompting anxieties that have compelled them to embrace Russia and the Syrian government.
The Syrian rebels once backed by the U.S. under former President Barack Obama now pose the greatest threat to Kurdish allies opposed by Turkey.
Syrian Kurdish fighters left behind by a U.S. exit are looking "for clear mechanisms to protect the northern border" by appealing to Syrian President Bashar al-Assad and Russia.
"I am very disappointed in the president that he would do this in this fashion," Rick Santorum said.
Trump's controversial decision led to the resignation of Secretary of Defense General Jim Mattis and Brett McGurk, the U.S. envoy to the coalition fighting the Islamic State militant group.
The Syrian Democratic Forces said Trump's decision to withdraw U.S. troops has "dangerous implications" for regional stability.
As U.S.-backed Syrian Kurds won a critical battle against ISIS in Syria, President Donald Trump reportedly warned his Turkish counterpart not to attack them.
Russia warned of a "rapidly deteriorating" situation in eastern Syria where U.S.-backed Kurds are struggling to defeat ISIS.
Russia Foreign Minister Sergey Lavrov said the U.S. is "illegally trying to create a quasi-state" for Kurds in eastern Syria.
The president appeared to be in high spirits Wednesday evening as he spoke to a crowded room of reporters.
U.S. Special Ops photos featured a French military vehicle in Syria's Deir Ezzor, but they were quickly pulled from social media.
The U.S. has already entered talks with France and the U.K. in what Russia fears could be a new set of strikes against its Syrian ally.
U.S. sanctions on Turkey have effectively split U.S. policy in the region.
America, as the planet's most powerful nation, can offer crucial help.
The Syrian Democratic Council, the political wing of U.S.-backed forces, called on others to support talks with Damascus.
The U.S.-backed Syrian Democratic Forces holds about 27 percent of the country's territory.