Ex-CIA director David Petraeus expressed deep regret on Friday over the affair that led to his resignation but insisted it did not interfere with his work on the Benghazi attack, lawmakers said.

"The General did not address any specifics of the affair," Democratic congressman James Langevin said as he emerged from a House Intelligence Committee hearing that heard testimony from General Petraeus.

"What he did say in his opening statement was that he deeply regrets the circumstances that led to his resignation," he added, referring to revelation that General Petraeus had an affair with his biographer Paula Broadwell.

General Petraeus' departure from the CIA sent shockwaves through Washington, where lawmakers are hosting several closed-door intelligence briefings on the September 11 attack on the US mission in Benghazi, Libya, that cost four American lives.

A bitter political feud has erupted in Washington since the assault, which left US ambassador Chris Stevens and three colleagues dead, with Republican lawmakers accusing president Barack Obama's administration of misleading the public about its causes.

Congress has summoned officials to explain why in the days after the attack they blamed the violence on a spontaneous protest triggered by an anti-Muslim video.

A car burns at the US consulate compound in Benghazi after the attack which killed Chris Stevens and three other Americans. ( AFP )

On September 14, General Petraeus told Congress that was the CIA's initial take on the events. Since then, the administration's position has evolved and it is now seen as a pre-meditated assault by an Al Qaeda-linked militia.

General Petraeus spoke at two of the hearings on Friday but avoided the media packs staking out both the House and Senate.

He told lawmakers he knew from the outset that the attack was the work of terrorists.

But according to Mr King General Petraeus had changed his analysis since September.

"General Petraeus' testimony today was from the start he had told us this was a terrorist attack or terrorist-involved from the start," he said.

"I told him in my questions I had a different recollection of that and the clear impression given was that the overwhelming matter of evidence is that it was a arose out of a spontaneous demonstration and was not a terrorist attack."

Mr King and other lawmakers said they were grateful for General Petraeus' testimony but, as he went into a second hearing with a senatorial committee, they made it clear they still had other questions for the administration.

Republicans have accused Washington's UN envoy Susan Rice of misleading the country by telling Sunday talk shows after the attack that it was part of a "spontaneous" protest against the anti-Islam video.

State Department and FBI probes into the attack are also under way, and secretary of state Hillary Clinton has agreed to testify before House and Senate hearings once her department finishes a review of events.

Ms Rice has been floated as a possible successor to Clinton, who is stepping down early next year, but some Republicans have threatened to block her appointment over Benghazi.

Affair impact

Jill Kelley and Paula Broadwell. ( Reuters )

Key players in the Petraeus scandal David Petraeus : Former chief of the CIA and four-star general in the US army.

: Former chief of the CIA and four-star general in the US army. Paula Broadwell : Mr Petraeus's biographer and mistress.

: Mr Petraeus's biographer and mistress. Jill Kelley : Sparked the FBI investigation after receiving threatening emails from Ms Broadwell.

: Sparked the FBI investigation after receiving threatening emails from Ms Broadwell. John Allen : US general investigated over between "20,000 to 30,000" pages of emails to Ms Kelley.

: US general investigated over between "20,000 to 30,000" pages of emails to Ms Kelley. Holly Petraeus: Married to Mr Petraeus for 37 years and the mother of his two adult children.

Republican Peter King said there was a single question in the House hearing about the Broadwell affair, addressing whether it had any impact on General Petraeus's testimony "and he said no."

Democrat lawmaker Dutch Ruppersberger agreed.

"He was very sorry that this incident occurred, and anything that occurred with respect to his personal situation had nothing to do with the way he handled Benghazi at all," the Maryland congressman said.

"And he also clarified... that his resignation wasn't because he didn't want to testify. Clearly that was not the case. End of story."

Mr King, who chairs the House Homeland Security Committee, acknowledged the awkwardness of essentially interrogating a friend whom he has known for nearly a decade and once urged to run for president.

"I consider him a friend, which made the questioning tough, to be honest with you," he told reporters.

"You realised that he's going through an awful lot. On the other hand, we had an obligation to find out what we could."

The Broadwell affair came to light as a result of an FBI inquiry that was launched in May when Jill Kelley, a 37-year-old Tampa socialite who hosted parties for officers at US Central Command in Florida, complained of threatening emails.

Agents traced the anonymous mails to Ms Broadwell's computer and found that she had been jealous of Ms Kelley's rapport with both General Petraeus and S commander of allied forces in Afghanistan, General John Allen.

While investigating cyber-stalking they uncovered sexually explicit emails between General Petraeus and Ms Broadwell.

General Allen was pulled into the drama this week when it was revealed he had written hundreds of emails to Ms Kelley, some of them reportedly "flirtatious", and the Pentagon launched an inquiry into his conduct.

AFP