On Tuesday, McCauley told The Washington Post that there was never a "quid pro quo" discussed between himself and State Department official Patrick Kennedy, and that the phrase appearing in the summary notes of an FBI investigation into Clinton's emails was due to a misunderstanding by another FBI official.

Kennedy called to say he needed a "favor" and McCauley responded with "good, I need a favor [too]".

But one of McCauley's colleagues characterized the conversation as a "quid pro quo".

He previously faced criticism from Congress for not standing in Clinton's way when she chose to use a private email server during her time in office, an arrangement that risked exposing classified secrets to foreign adversaries and concealing her correspondence from legitimate public disclosure requests.

Former FBI official Brian McCauley told the New York Times on Tuesday that he had initiated the conversation with Kennedy.

Undersecretary of State for Management, Patrick Kennedy.

Kennedy said in his statement that he thought the email should have been redacted but not because it was classified.

At the time, administration officials acknowledged interagency disagreements about whether certain information in the emails was classified, disagreements that the State Department said were contributing to the slow processing of their public release under the Freedom of Information Act. I need a favor, ' " McCauley recalled in the interview. The Democratic candidate's critics have suggested that the conversation between the State Department and the Federal Bureau of Investigation demonstrated inappropriate collusion to benefit Clinton.

A top former Justice Department privacy officer on Wednesday called it "extremely unlikely" that a senior US diplomat would normally discuss the nuances of classification levels of one of Hillary Clinton's emails about Benghazi with the deputy assistant director of the FBI's global operations bureau. McCauley said he agreed to help but only if the State Department opened two spots in the Baghdad embassy.

"As I understand, those were her personal belongings she brought from home to decorate her offices and then took them back again", he explained.

"To learn that a senior State Department official may have attempted to make a backroom deal to cover up the extent to which our national security was put at risk by Secretary Clinton's use of a secret email server is shocking and warrants an immediate review by your office", RNC chief counsel John Philippe Jr. wrote to the State Department Inspector General. "There was no quid pro quo even suggested or any kind of bargain laid on the table". It had been forwarded to Clinton's private email address by Jake Sullivan, one of her top aides and the department's director of policy planning, who was using his government email account. The email was released with a notation that material was classified and redacted because it would reveal confidential sources or information from a foreign government. On Monday, the Republican chairmen of the House Oversight and Intelligence committees also called on Kennedy to resign. "The FBI did not change its position on classifying the email and the department did not change its position on the appropriate number of FBI officials to authorize".