(NBC NEWS) -- The Defense Department's inspector general has found that allegations that Gen. John Allen engaged in inappropriate behavior in emails he exchanged with Tampa, Fla., socialite Jill Kelley were unsubstantiated.
"The IG cleared him," a defense official told NBC News, speaking on condition of anonymity.
Allen, the current commander of NATO forces in Afghanistan, has been nominated to be Supreme Allied Commander in Europe, but that promotion was put on hold when the IG investigation began. The defense official stressed that no decision has been made yet on whether his nomination will go forward again.
Allen's nomination was jeopardized in mid-November when it was revealed that he had exchanged emails with Kelley that some Pentagon officials at the time characterized as "inappropriate" and "flirtatious."
Allen had met Kelley when he was commander of MacDill Air Force Base outside Tampa, where she served as a volunteer "social liaison."
U.S. Gen. John Allen, in an April 28, 2011 file photo.
She inadvertently drew him into the scandal that led to the resignation of former CIA Director David Petraeus by complaining to an FBI agent with whom she was acquainted about anonymous emails referencing Petraeus. Among those emails was one that Allen had forwarded to her in the belief that she had sent it to him as a joke, officials told NBC News at the time.
FBI agents eventually traced the allegedly threatening emails to Paula Broadwell, Petraeus' biographer. That investigation also led to evidence of an extramarital affair between Petraeus and Broadwell, prompting his resignation on Nov. 7. Days later, Defense Secretary Leon Panetta announced the investigation into Allen's relationship with Kelley.
The inspector general's investigation does not determine guilt or innocence. Rather, it decides whether an allegation is substantiated or not. Even if the finding is that the allegation is unsubstantiated, the IG can still make a recommendation that can harm an officer's career. (For example, the IG could find there was no evidence of an affair between Allen and Kelley, but there was evidence of inappropriate behavior.)
Jim Miklaszewski is NBC News' Chief Pentagon Correspondent; Courtney Kube is an NBC News producer at the Pentagon. Mike Brunker, NBC News investigations editor, contributed to this report.