Michael Biesecker

Associated Press

Sen. Chuck Grassley of Iowa asked the FBI on Wednesday to correct what he called its "mistake" of restricting access to unclassified files from its closed investigation into former Secretary of State Hillary Clinton's use of a private email server.

The Iowa Republican, who chairs the Senate Judiciary Committee, urged FBI Director James Comey to send his committee any unclassified records involving the investigation into the Democratic presidential nominee. Grassley set a deadline of Friday.

Responding to requests from GOP House members, the FBI on Aug. 16 delivered two large binders containing both classified and unclassified documents to a secure room on Capitol Hill typically reserved for the nation's most closely guarded secrets. Documents containing classified information are included with those marked by the FBI as "Unclassified/For Official Use."

Grassley said that by comingling the documents and locking them away the FBI violated an executive order dictating the proper handling classified materials.

"The FBI is not following its legal responsibility and is impeding the ability of Judiciary Committee members and staff to work with the unclassified documents," Grassley wrote.

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The FBI did not immediately respond to emails from the Associated Press asking to discuss Grassley's demand.

The FBI in July closed the agency's yearlong investigation into whether Clinton and her top aides mishandled classified information that flowed through a private email server located in the basement of her New York home. Though he described Clinton's actions as "extremely careless," Comey said his agents found no evidence to support criminal charges.

Republicans said Clinton lied to Congress about her handling of emails when she testified last October before a House panel investigating the deadly 2012 attacks in Benghazi, Libya. The GOP is pressing the Justice Department to open a new investigation into whether Clinton committed perjury.

FBI case files are typically kept confidential after an investigation is closed without a recommendation for charges, and the Clinton documents were sent to Congress accompanied by written warnings not to leak the information.

The documents from the FBI's investigation are being kept in a Sensitive Compartmented Information Facility, known within the intelligence community as a SCIF.

Access to the guarded room is strictly restricted. Only those with high-level security clearances can view the unredacted files containing classified information.

"It is improper to bundle unclassified information with classified information in this manner in an attempt to impose controls on unclassified documents as though they were classified," Grassley wrote in his letter to the FBI director. "It also raises serious constitutional separation of powers issues when the imposition of such document controls interferes with the independent oversight function of the Judiciary Committee."