Only 11 days ago, McGurk had said it would be “reckless” to consider IS defeated and therefore would be unwise to bring American forces home. He decided to speed up his plan to leave in mid-February.

McGurk, appointed to the post by President Barack Obama in 2015 and retained by Trump, said in his resignation letter that the militants were on the run, but not yet defeated, and that the premature pullout of American forces from Syria would create the conditions that gave rise to IS. McGurk also cited gains in accelerating the campaign against IS, but that the work was not yet done.

His letter, submitted Friday to Secretary of State Mike Pompeo, was described to The Associated Press on Saturday by an official familiar with its contents. The official was not authorized to publicly discuss the matter before the letter was released and spoke on condition of anonymity.

Trump is acting to pull all 2,000 US troops from Syria and has now declared victory over IS, contradicting his own experts’ assessments. Many lawmakers have called his action rash and dangerous.

Mattis, perhaps the most respected foreign policy official in the administration, announced on Thursday that he will leave by the end of February. He told Trump in a letter that he was departing because “you have a right to have a Secretary of Defense whose views are better aligned with yours.”

Reporter’s code: 50101