(CNN) The Trump administration is walking back the notion of an imminent pullout of US forces from Syria, promising to remain until there is an "enduring defeat" of ISIS.

"This means we are not in a hurry to pull out," said Ambassador Jim Jeffrey, the newly appointed US special representative, noting that creating conditions in Syria where ISIS or another terrorist group can't return may take a while.

Jeffrey, a former US ambassador to Turkey, said the US was "shifting its position" to remain active in the country and to push for a complete withdrawal of all Iranian forces from Syrian territory.

Though President Donald Trump has previously expressed a desire to pull US forces out of Syria, Jeffrey said the President "is on board" with the new approach.

Jeffrey spoke to reporters as Russian forces prepare for an all-out assault on Syria's Idlib province, the last rebel stronghold. Trump and his top officials have called attention to the impending Syrian government offensive in recent days, warning the Syrian regime and its backers Russia and Iran not to use chemical weapons or recklessly cause civilian deaths.

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