WASHINGTON — The sex scandal that led to CIA Director David Petraeus' downfall widened Tuesday with word the top U.S. commander in Afghanistan is under investigation for thousands of alleged "inappropriate communications" with another woman involved in the case.

Even as the FBI prepared a timeline for Congress about the investigation that brought to light Petraeus' extramarital affair with his biographer, Paula Broadwell, Defense Secretary Leon Panetta revealed that the Pentagon had begun an internal investigation into emails from Gen. John Allen to a Florida woman involved in the case.

Allen succeeded Petraeus as the top American commander in Afghanistan in July 2011, and his nomination to become the next commander of U.S. European Command and the commander of NATO forces in Europe has now been put on hold, as the scandal seemed certain to ensnare another acclaimed military figure.