Washington: A probe by Federal Bureau of Investigation revealed that Central Intelligence Agency (CIA) director David Petraeus was having an affair with his biographer, Paula Broadwell, said a report.
Petraeus resigned on Friday after admitting the affair.
The abrupt departure of celebrated general has sent shock waves across Washington`s intelligence and political communities.
The retired four-star general, who had a distinguished 37-year career in the military prior to joining the CIA, helping turn the tide against insurgents while commanding forces in Iraq and Afghanistan, became CIA chief in September 2011.
Praised by both sides of the political divide for his handling of the Iraq and Afghanistan wars, Petraeus, 60, was at one time speculated as a possible Republican challenger to President Barack Obama.
The FBI had a tip he was involved with Broadwell and investigated the alleged affair to determine whether it posed a security risk, CNN reported citing an unnamed official.
The FBI was not investigating Petraeus for wrongdoing. The concern was that he potentially could be blackmailed or put "in a vulnerable spot”, the official said.
The agency discovered the relationship by monitoring Petraeus` e-mails, after being alerted Broadwell may have had access to his personal e-mail account.
Broadwell spent a year with Petraeus in Afghanistan interviewing him for the book she co-wrote, "All In: The Education of General David Petraeus”.
It is not clear whether Broadwell is the woman with whom Petraeus has admitted having an affair, CNN said."After being married for over 37 years, I showed extremely poor judgment by engaging in an extramarital affair. Such behaviour is unacceptable, both as a husband and as the leader of an organisation such as ours," Petraeus said in a letter to colleagues, explaining his decision to step down.
"Teddy Roosevelt once observed that life`s greatest gift is the opportunity to work hard at work worth doing. I will always treasure my opportunity to have done that with you and I will always regret the circumstances that brought that work with you to an end," he said.
Obama, who has accepted the CIA chief`s resignation, said: "By any measure, he was one of the outstanding general officers of his generation, helping our military adapt to new challenges, and leading our men and women in uniform through a remarkable period of service in Iraq and Afghanistan, where he helped our nation put those wars on a path to a responsible end."
"As director of the Central Intelligence Agency, he has continued to serve with characteristic intellectual rigor, dedication and patriotism."
(With IANS inputs)