FBI Director James Comey refused to attend a classified briefing with the House Oversight Committee despite receiving an invitation to testify about the bureau's reluctance to disclose thousands of pages of evidence compiled in its year-long investigation of Hillary Clinton's private email use.

Rep. Elijah Cummings, the committee's top Democrat, said Monday that Comey had declined to appear at the meeting because he had "already bent over backwards" to explain the FBI's decision-making in the Clinton email case.

But Rep. Jason Chaffetz, chairman of the Oversight Committee, disputed the suggestion that he had invited Comey to the public hearing on redactions in notes from the Clinton email case, noting he had discussed specific points of concern in a personal phone call with the FBI director but had not issued a subpoena for Comey's presence at the hearing.

Chaffetz called the hearing to question officials about why whole and partial documents had been withheld from Congress, including unclassified files.

"I don't expect to have to issue a subpoena to see unclassified information," Chaffetz said.

"As far as we can tell, the redactions are covering information commonly given to Congress," he added, suggesting some of the details withheld from the FBI's notes were simply embarassing for the agencies or the people involved and were not sensitive enough to warrant redaction.

Cummings accused the Republican chairman of the Oversight Committee of first inviting witnesses to a classified hearing about the FBI's redactions before moving at the last minute to make it a public meeting. Comey had been invited by committee Republicans to a classified briefing held last week, but no one from the administration appeared.

Chaffetz demanded the FBI provide its full investigative file to Congress rather than the "hand-picked" elements shared with lawmakers to date. During a heated exchange with an FBI agent present at the hearing, Chaffetz issued a subpoena for summaries of all interviews conducted with witnesses throughout the probe.

The Utah Republican demanded representatives of the State Department, FBI, Justice Department and three intelligence agencies — some of whom appeared under threat of subpoena— outline what records the government felt compelled to withhold from Congress and explain why they felt members should not be permitted to read those documents.

Administration officials from the Justice and State departments stated for the record that they had appeared voluntarily.

The FBI's decision to release a 58-page summary on the Friday before Labor Day rankled Republicans who questioned the bureau's reasoning for declining to publish any additional materials from its volume of documentary evidence. Critics blasted the timing of that release after the summary revealed scathing new details about Clinton aides' destruction of records under subpoena, among other findings.