Special Presidential Envoy for the Global Coalition to Counter IS, retired Gen. John R. Allen prepares to testify on Capitol Hill in Washington, Wednesday, Feb. 25.

The U.S. special envoy for countering the Islamic State of Iraq and Syria (ISIS) militant group, retired General John Allen, plans to step down for personal reasons, a U.S. official said on Tuesday.

Allen, a retired U.S. Marine four star general and a former commander of NATO and U.S. Forces in Afghanistan, had originally agreed to serve in the job for six months and has done it for a year, said the official who spoke on condition of anonymity.

While acknowledging disagreements within Washington over U.S. policy toward the militant group, which has seized control of parts of Iraq and Syria, the U.S. official said Allen’s plan to step down reflected personal, not professional, factors.

The Syrian civil war has raged for more than four years, creating a vacuum in Syria that the ISIS extremist group has exploited to seize territory there and in neighboring Iraq.

Allen’s job included rallying a U.S.-led coalition that has carried out air strikes against ISIS fighters in both nations. Asked if Allen had told colleagues he planned to leave, State Department spokesman Mark Toner did not answer directly, telling reporters that he “remains focused on his duties.”

Allen’s plans to step down were first reported on Bloomberg View.