Washington (CNN) The former US envoy for the anti-ISIS coalition said Monday that "ISIS is not defeated" nearly a month after President Donald Trump announced he was withdrawing troops from Syria on the premise that the US had defeated the terrorist group.

Brett McGurk, who resigned last month because of Trump's decision, made the comment in an interview with CNN's Christiane Amanpour just hours after an attack targeting US forces in the country occurred. It also comes just days after a deadly attack by ISIS in northern Syria killed four Americans and at least 10 other people in the city of Manbij. No Americans were killed in Monday's attack, and the US did not immediately blame a particular terrorist group.

"In early December, Secretary Mattis and I met with all the military contributors of our coalition, including many countries that had been attacked from ISIS out of Syria and the unanimous view is that ISIS is not defeated, this mission is not over," McGurk told Amanpour. "I do not think there would be a single expert that would walk in the Oval Office and tell the President that this is over."

"The irony is that defeating the Islamic State is what the president said from the beginning was his goal. In 2016, he vowed to 'knock the hell out of ISIS.' His recent choices, unfortunately, are already giving the Islamic State — and other American adversaries — new life," McGurk wrote.

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