General John Allen, the commander of US and NATO forces in Afghanistan, was cleared by Pentagon investigators of allegations of professional misconduct over e-mail exchanges with a Florida socialite, US officials said on Tuesday.

The decision by the Defense Department's Inspector General helps lift a cloud that has hung over Allen, who is married and has two daughters, ever since he became indirectly ensnared in the scandal that forced David Petraeus to resign as CIA director in November.

It could also resurrect the four-star general's military career although a US official told Reuters that, as of late Tuesday, no decision had been made on whether to proceed with Allen's nomination to become the top US military commander in Europe.

President Barack Obama put that nomination on hold when the investigation was announced in November, even as he expressed confidence in Allen's ability to serve out the final months of his command in Afghanistan.

"With the investigation having only recently concluded, no decisions have been made on moving the nomination forward," the official said, speaking on condition of anonymity. "But it's entirely possible that it could move forward in the days or weeks ahead."

The Pentagon inquiry centered on e-mails between Allen and Jill Kelley, a Tampa, Florida, resident who knew Allen when he served as the No. 2 officer at the US military's Tampa-based Central Command from July 2008 to June 2011.

Kelley, in a piece written with her husband Scott and published on the Washington Post website, said "the insinuation that Jill was involved in an extramarital affair is as preposterous as it is hurtful to our family."

The investigation also likely took its toll on Allen. Minimally, it limited his contact with the media as he was wrapping up his time in Afghanistan and preparing options for Obama on the future US military presence once NATO declares the combat mission over at the end of 2014.

Pentagon Chief Leon Panetta was described by his spokesman to be "pleased to learn that allegations of professional misconduct were not substantiated by the investigation."

"The Secretary has complete confidence in the continued leadership of General Allen," spokesman George Little added.

If his nomination does proceed, Allen could still potentially face questions about the e-mail exchanges at a Senate confirmation hearing for the job as head of US European Command and Supreme Allied Commander Europe.

Reuters