Former CIA director David Petraeus has denied passing classified documents to his lover, Paula Broadwell, as the FBI investigation focuses on how the general's biographer came to have restricted material on a personal computer and in her house.
Petraeus also told CNN that his resignation was solely the result of the affair and was not linked, as some Republicans have hinted, to the CIA's role during the Benghazi attack in which the US ambassador to Libya, Chris Stevens, and three other Americans, including two CIA security men, were killed.
The CIA said it had opened an "exploratory" investigation into the conduct of Petraeus. "At the CIA we are constantly reviewing our performance. If there are lessons to be learned from this case, we'll use them to improve," a CIA spokesperson said in a statement. "But we're not getting ahead of ourselves; an investigation is exploratory and doesn't presuppose any particular outcome."
Petraeus has agreed to give evidence on Friday to congressional intelligence committees looking into the security failures around Stevens' death, including allegations that the state department turned down appeals from US officials in Libya for more protection, and accusations that the CIA and other agencies failed to heed warning signs of an attack.
The closed-door hearings opened with appearances by Petraeus's replacement, acting CIA director Michael Morell, and the national intelligence director, James Clapper.
CNN did not directly quote Petraeus. It said he had had a conversation with one of its reporters, Kyra Phillips, who has previously interviewed him. She said that although Petraeus was no longer formally required to testify to congressional intelligence committees about the Benghazi attack once he resigned as CIA director, he was keen to do so.
"He said this has nothing to do with Benghazi, and he wants to testify," she said on CNN.
Petraeus's affair prompted the US defence secretary, Leon Panetta, to order a review of ethics training for military officers. The FBI is scrutinising classified material discovered in Broadwell's house and on her computer. But Phillips said Petraeus denied giving secret documents to her.
The Pentagon withdrew Broadwell's security clearance as a lieutenant colonel in the military intelligence reserve as the focus of the FBI investigation shifted to how she came to have classified documents. Her security clearance gave her access to "secret" and "top secret" material. However, it would not necessarily have permitted her to keep hold of it.
Concerns that Petraeus may have spoken to Broadwell about secret information were raised after it was revealed that in a speech at the University of Denver last month, Broadwell said the Benghazi attack on 11 September was prompted by the CIA holding militiamen prisoner there. The CIA has denied the claim.
The intelligence committees of both houses of Congress are keen to speak to Petraeus about what the CIA told the White House in the immediate aftermath of the Benghazi attack as well as whether it had picked up warnings of an imminent assault and security failings.
Republican ire has focused on Susan Rice, the US ambassador to the UN, who said in television interviews five days after the attack that it was an angry, spontaneous response to an anti-Muslim video on the web which prompted protests in Egypt and other countries.
Senator John McCain has accused the administration of playing down links between the attackers and al-Qaida and of denying that the assault was a terrorist attack.
Barack Obama fired back, vigorously defending Rice by saying her statements reflected the intelligence information available at the time.
CBS reported that it obtained the CIA talking points given to Rice, which were also supplied to the House of Representatives intelligence committee ahead of the hearing, in which no reference was made to the Benghazi assault being a terrorist attack.
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