There is "no evidence" of national security breaches in connection with the resignation last week of US Central Intelligence Agency (CIA) chief David Petraeus over an extramarital affair, US President Barack Obama has declared.

"I have no evidence at this point, from what I've seen, that classified information was disclosed that would have had a negative impact on our national security," Obama told reporters in his first news conference since his reelection last week at the East Room of the White House.

The reelected US President said he is "withholding judgment" on a decision by the US Federal Bureau of Investigation (FBI) to wait until after the Nov. 6 election to inform the White House of Petraeus' affair with his biographer, Paula Broadwell.

The FBI is said to have learned of the illicit relationship this past summer amid an investigation into Broadwell's alleged cyber-harassment of a woman she reportedly perceived as a rival for the US spy chief's affections.

Law enforcement officials cited by US media have said they withheld information about the case from top US officials because it had not reached the threshold of a national security concern.

"It's also possible that had we been told, you'd be sitting here asking: 'Why were you interfering in a criminal investigation?'" Obama told reporters.

The Petraeus case has also ensnared Gen. John Allen, the top American commander in Afghanistan, who is being investigated for possible "inappropriate communications" with a Florida socialite allegedly harassed by Broadwell via anonymous emails.

Petraeus is scheduled to testify before a US Senate committee on Thursday about the Sept. 11 attack on an American embassy compound in Benghazi, which left four Americans diplomats dead, including the US ambassador to Libya, Christopher Stevens.

Republicans have accused the Obama administration of failing to adequately protect the US diplomats killed in the Benghazi attack, and they have criticized the White House for giving a conflicting account of the circumstances surrounding the attack. The US government has since stated the assault appears to have been carefully planned by armed militants.

The lightning rod for this criticism has been Susan Rice, Obama's ambassador to the United Nations, who publicly suggested shortly after the attack that militants stormed the compound amid a protest over an anti-Islam film posted on YouTube.

Republican attempts to smear Rice's reputation in connection with the Benghazi attack are "outrageous," Obama said.

Rice had "nothing to do with Benghazi" and made her comments on the attack "based on intelligence that she had received," Obama added.