According to the daily, which cited a senior US official, Allen exchanged “a few hundred emails” with Kelley over the years when he was deputy commander of US Central Command in Tampa, Florida and she was organizing local parties.

In the mails Allen called Kelley “sweetheart,” a common term of endearment in his native Virginia, but the pair did not have a romantic connection, the official told the Post, speaking on condition of anonymity.

But another US officer told AFP the huge extent of the correspondence could have constituted a “violation of military rules” or even “conduct unbecoming of an officer,” which could lead to Allen being sanctioned.

Allen's promotion to the post of Nato supreme commander has been put on hold while the Pentagon investigates the correspondence between him and Kelley, a married woman who helped organize social events at MacGill Air Force Base.

Kelley inadvertently triggered a scandal that forced former general Petraeus to resign from the CIA last week, when she complained to a friend who is an FBI agent that she had received threatening anonymous emails.

The FBI launched an investigation and traced the mails back to Paula Broadwell, a 40-year-old army reservist and Petraeus' biographer, who was apparently jealous of Kelley's close social relations with the generals.

Accessing her emails, the FBI agents discovered that Petraeus and Broadwell, both married, had had a sexual relationship. Petraeus, the most renowned officer of his generation, resigned last week.

According to the officer cited in the Post report, Broadwell had also sent an anonymous mail to Allen about Kelley. He discussed the mail with Kelley, but did not realize it had come from Broadwell.