FBI agents interviewed ex-CIA chief David Petraeus to probe whether secret files had been passed to the woman at the center of the scandal that brought him down, USA Today reported.

Petraeus, America's most celebrated military leader in a generation, stepped down in November as head of the spy agency after admitting to an affair with his biographer Paula Broadwell.

The move ended a storied career marked by his tenure as military commander in the wars in Iraq and Afghanistan.

USA Today cited a federal law enforcement official as saying that the interview at Petraeus's home in northern Virginia just outside Washington was part of an ongoing investigation into whether Broadwell had received classified information or whether such files were kept at an unauthorized location.

The investigation is taking considerable time to complete, according to the official.

FBI spokeswoman Jacqueline Maguire told AFP that agents conducted "law enforcement activity" in northern Virginia. The bureau would not provide any further details on the matter.

And CIA spokeswoman Jennifer Youngblood told AFP "the agency does not comment on active investigations."

"CIA is fully cooperating with the FBI," she added.

The CIA declined to comment on any other related queries.

Petraeus made his first public speech last week since he quit over the extramarital affair, addressing more than 600 veterans and Reserve Officers' Training Corps students, hosted by the University of Southern California at a Los Angeles hotel.

He apologized to his friends, family and supporters for the "pain" caused by his relationship with Broadwell, pledging to try to "make amends to those I have hurt and let down."

The scandal erupted after Florida socialite Jill Kelley complained to the FBI that she had received menacing emails from an anonymous sender.

The emails turned out to be from Paula Broadwell, an Army reservist who wrote a glowing biography of Petraeus's tenure as a top military commander.

Authorities then stumbled upon evidence of Broadwell's affair with Petraeus, as well as exchanges between Kelley and the four-star general in charge of the war in Afghanistan, John Allen.

Allen was investigated and later cleared by the Pentagon's inspector general for a series of emails he had sent to Kelley. Although President Barack Obama had chosen Allen to take up command of NATO forces in Europe, he chose to retire instead.