"The administration is working with Colonel Harvey to identify positions in which his background and expertise can be best utilized," the White House said in a statement announcing the departure.
Harvey was seen as one of the few allies of ousted national security advisor Michael Flynn, who remained in the White House.
In recent months he had complained in private about his waning influence as he wrestled with competing US interests in Syria and elsewhere.
Hawkish on Iran -- thanks to experience countering Shia militias in Iraq -- he also viewed the fight against the Islamic State as a key US priority.
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