The US national security establishment was rocked by further personal scandal yesterday when the Pentagon announced that its top Afghanistan commander was under investigation for potentially “inappropriate communication” with one of the women at the centre of the controversy that brought down the head of the Central Intelligence Agency.

The Pentagon said it was examining email contacts between General John Allen and Jill Kelley, who does volunteer work at a military base in Tampa, Florida. Ms Kelley’s complaints about email harassment by another woman led to the resignation of CIA director David Petraeus.

The Pentagon gave no information about the nature of any potential violations, although a confirmation hearing scheduled for tomorrow to consider Gen Allen’s next promotion has been put on hold. He had been nominated to become the next commander of US forces in Europe, one of the military’s most prestigious positions.