The top US commander in Afghanistan, Gen John Allen, is being investigated for allegedly sending "inappropriate emails" to a woman at the centre of a scandal which ended the career of CIA head David Petraeus.
The emails were said to be to Jill Kelley, whose complaint led the FBI to uncover Gen Petraeus's extramarital affair with Paula Broadwell.
Gen Allen denies any wrongdoing.
His nomination to head Nato in Europe is now on hold, the White House says.
Gen Allen was due to face a Senate confirmation hearing for the post of Supreme Allied Commander in Europe, but that has been suspended at the request of Defence Secretary Leon Panetta, a spokesman said.
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