With David Petraeus telling a US network he did not pass on classified information to his former lover, Channel 4 News untangles the links between key players in the scandal engulfing the CIA.

In an interview with CNN's sister network HLN, David Petraeus said that he resigned because of his affair with Paula Broadwell and not because of September's deadly attack on the US consulate in Libya.

General Petraeus is due to be quizzed behind closed doors on Friday about the violence in Benghazi which left four Americans dead.

Questions about the adequacy of security, the US response, and the administration's initial public comments have led to a growing rift between Republicans and President Barack Obama over where the fault lies.

"Director Petraeus went to Tripoli, he interviewed many of the people as I understand it, that were involved. So the opportunity to get his views, I think is very important," said Senate Intelligence Committee Chairman Dianne Feinstein.

The CIA says it has started an "exploratory" investigation into the Petraeus' affair, building on the FBI's probe. Law enforcement officials have said they believe the FBI investigation is likely to end without criminal charges.

David Petraeus told HLN that he did not pass on any classified information to Paula Broadwell during their affair and that he has not spoken to her since news of it broke.

The scandal has cast a spotlight on the private lives of some of the nation's top national security officials.

The commander of US and Nato forces in Afghanistan, Marine General John Allen, now faces a Pentagon inspector general's review of what sources describe as "flirtatious" emails with Tampa socialite Jill Kelley - a friend of the Petraeus family.

President Obama has publicly backed General Allen saying he has "faith" in the man chosen to be the next Nato commander in Europe.