Hillary Clinton's campaign responded angrily to news that the FBI had given Congress documents pertaining to its investigation of her private emails, and characterized the move as a part of a partisan witch-hunt.

"This is an extraordinarily rare step that was sought solely by Republicans for the purposes of further second-guessing the career professionals at the FBI," Clinton spokesman Brian Fallon said in a statement.

"We believe that if these materials are going to be shared outside the Justice Department, they should be released widely so that the public can see them for themselves, rather than allow Republicans to mischaracterize them through selective, partisan leaks," he added.

FBI agents handed the House Oversight Committee a "number of documents" Tuesday regarding the law enforcement agency's investigation of Clinton's use of an unauthorized private email server when she worked at the State Department.

"The records were marked 'secret,' the second-highest level of classification given to government documents," a committee aide told the Washington Examiner.

"Committee staff is currently reviewing the information," the aide. "There are no further details at this time."

FBI Director James Comey announced last month that his agency would seek no charges against Clinton for her use of the private email server. However, during a highly anticipated press conference, he also revealed several notable details regarding Clinton's private emails.

Comey said Clinton didn't turn everything over to the State Department as she claimed, and said investigators found thousands of additional work-related emails on her private servers.

"The FBI also discovered several thousand work-related emails that were not in the group of 30,000 that were returned by Secretary Clinton to State in 2014," he said.

Of the additional emails uncovered by investigators, three "were classified at the time they were sent or received, one at the secret level and two at the confidential level," which contradicts Clinton's earlier claim that she never handled classified information over her private servers.

"From the group of 30,000 emails returned to the State Department, 110 emails in 52 email chains have been determined by the owning agency to contain classified information at the time they were sent or received," Comey said.

Comey appeared later before the House Oversight Committee and said that the FBI's three-hour interview with Clinton was neither transcribed nor taken under oath.