Outgoing Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE has signed the order to withdraw U.S. troops from Syria, an official confirmed to CNN on Sunday.

"The execute order for Syria has been signed," a defense official told the network.

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The order lays out the logistics of the withdrawal, defining how and when it will take place. The officials declined to share details with CNN.

The withdrawal could reportedly begin within the next few weeks.

Trump surprised Pentagon officials last week by announcing that the U.S. would withdraw the roughly 2,000 troops from Syria. Trump on Twitter claimed that the forces had successfully "defeated ISIS," a claim that some defense experts within his own administration have doubted.

Mattis resigned on Thursday, one day after the announcement. Mattis in his resignation letter cited policy differences with Trump, saying and the president do not share the same priorities.

Multiple top Republicans, including Sen. Lindsey Graham (R-S.C.), met the U.S. withdrawal from Syria with criticism. Graham called it an "Obama-like mistake."

Brett McGurk, the special presidential envoy for the Global Coalition to Defeat ISIS at the State Department, also submitted his resignation on Friday due to his disagreement with the president's decision to withdraw the troops.

White House press secretary Sarah Huckabee Sanders in a statement last week said the U.S. plans to start bringing troops home "as we transition to the next phase of this campaign."