The chairman of the House Oversight Committee is demanding the FBI provide additional details about the unauthorized individuals who may have handled Hillary Clinton's classified emails before the Justice Department took custody of her private server.

In a letter to FBI Director James Comey made public Tuesday, Rep. Jason Chaffetz, R-Utah, asked for documentation that the FBI had looked into allegations that members of Clinton's legal team stored classified materials in their offices without maintaining any level of security clearance.

Chaffetz said he first requested the FBI's investigative files in writing on July 11. However, he said the notes provided to Congress by the law enforcement agency last week did not shed light on the role Clinton's lawyers may have played in exposing sensitive material while those emails languished for months on a thumb drive in a desk drawer.

"There's a great deal of concern about an uncleared person ... potentially having access," Comey said last month of the attorneys' handling of the emails.

The FBI director testified in a hearing before the House Oversight Committee that "more than two, less than 10" individuals without a proper security clearance had access to Clinton's classified emails.

While the State Department labeled more than 1,000 emails as classified before releasing them to the public last year, Comey said his agents recovered more than 100 additional records that should have been considered classified at the time they were written.

In addition to Clinton's legal team, employees at three technology companies that supported the private network may have inadvertently accessed the classified records before the FBI investigation began last summer.

Republican lawmakers issued subpoenas to those three firms on Monday.