The David Petraeus sex scandal escalated into a national crisis last night (Tuesday) as "flirtatious" correspondence emerged between America's top commander in Afghanistan and one of two women implicated in the row that has already forced the CIA chief's resignation.
General John Allen was placed under investigation after the FBI uncovered a cache of 20,000 to 30,000 pages of emails with Jill Kelley, the woman whose complaints about email harassment led to the discovery that Petraeus was having an affair.
The messages were discovered by agents looking into Petraeus's affair with his biographer and forced the White House to postpone plans to promote General Allen as the next new Nato supreme allied commander for Europe.
General Allen, 58, reportedly "strongly denied" having any affair with Kelley, according to a senior Pentagon official quoted in the Washington Post.
The official said the correspondence consisted of a "few hundred" emails that were mostly about "routine stuff".
However another official, explaining the need for an investigation, said the email exchanges might be construed as "flirtatious" and "potentially inappropriate".
Kelley, 37, is described as a "vivacious" social planner who organised parties for officers at the US Central Command in Tampa, Florida, where both General Allen and Petraeus, 60, a former four-star general, served together between 2008 and 2010.
Both men became close to her and even agreed to write letters testifying to the character of her twin sister, Natalie, as she went through an ugly divorce battle in Washington DC.
Kelley provoked the investigation that led to the downfall of Petraeus after she complained about receiving harassing anonymous email that were traced back to Paula Broadwell, 40, the CIA chief's mistress and the author of a book about his career.
Broadwell may also have sent an anonymous email to General Allen as part of her alleged campaign to tarnish Kelley's reputation in the eyes of the two military commanders, CNN reported.
During the course of the investigation, FBI officials searched Kelley's inbox, as part of a policy to cast a wide net in cybercrimes cases, and discovered messages from General Allen, according to the New York Times.
An aide close to GeneralAllen said that Kelley was "good friends" with the general's wife, Kathy, and speculated that a misunderstanding may have arisen as a result of Gen Allen's habit of addressing women as "sweetheart" - an innocent term of endearment often used by those from the America South.
"He's embarrassed by this," the senior official told the Washington Post, adding: "He's never been alone with her. Did he have an affair? No."
But another defence department official said the quantity of alleged correspondence raised suspicions of "conduct unbecoming of an officer".
The US military has strict rules limiting non-business contacts and a criminal code that lists adultery as an offence.
Leon Panetta, the US defence secretary, praised General Allen for his work in Afghanistan and said he would remain in position as head of the International Stablisation Assistance Force (ISAF) until the "facts are determined".
"His leadership has been instrumental in achieving the significant progress that ISAF, working alongside our Afghan partners, has made in bringing greater security to the Afghan people," Panetta said.
He added that his work had been vital in "ensuring that Afghanistan never again becomes a safe haven for terrorists; he is entitled to due process in this matter".
Jay Carney, the White House press secretary, said President Barack Obama "has faith in General Allen and believes he is doing and has done an excellent job at ISAF".
Tommy Vietor, the national security spokesman, confirmed that Obama had delayed General Allen's nomination to the Nato post, adding that he "remains focused on fully supporting our extraordinary troops and coalition partners in Afghanistan".
Peter King, the Republican chairman of the House homeland security committee, described the involvement of the two generals as "just tragic".
"This has the elements in some ways of a Hollywood movie or a trashy novel but the bottom line is you're talking about families and outstanding military leaders and the impact it has on the country," he told NBC.