The FBI submitted a classified declaration to a federal court judge late Friday explaining details about the bureau's "pending investigation" into the use of a private email server by Democratic presidential frontrunner Hillary Clinton. The declaration addresses why the FBI can't publicly release any records about its probe in response to a Freedom of Information Act (FOIA) lawsuit filed by VICE News.

In a separate public declaration, David Hardy, the chief of the FBI's FOIA office, said there are a number of documents exchanged between the FBI and the State Department relating to the FBI's ongoing investigation of Clinton's use of a private email server, which stored all of the official government emails Clinton sent and received during her tenure as Secretary of State. But the FBI, which consulted with attorneys within its Office of General Counsel "who are providing legal support to the pending investigation," cannot divulge any of them without "adversely affecting" the integrity of its investigation.

Some of the documents at issue concern "server equipment and related devices obtained from former Secretary Clinton," Hardy said. The documents "consist of memoranda from the FBI to the Department of State regarding evidence. The purpose of these communications with the Department of State was to solicit assistance in furtherance of the FBI's investigation."

VICE News sought a wide-range of records from the FBI last December related to Clinton's private email server. Specifically, we asked the FBI for any emails and other documents retrieved from her server, thumb drive, and any other electronic equipment that has not been publicly disclosed; any correspondence and other documents between the FBI and Clinton or her representatives; correspondence between the FBI and the State Department about Clinton's server; and any documents memorializing authorizations granted to the FBI to disclose to the media what the bureau seized from her server. In his declaration, Hardy said the FBI does not have any documents showing that the bureau communicated with Clinton or her aides nor does the FBI have any records about disclosures to the media. The FBI has asked US District Court Judge Randolph Moss to dismiss VICE News' FOIA lawsuit on grounds that the documents it does have about Clinton's private email server are located in files pertaining to a pending investigation that is exempt from disclosure because their release would interfere with active law enforcement proceedings.

"Materials that were retrieved from any server equipment and related devices obtained from former Secretary Clinton for the investigation, which would be responsive to [VICE News' FOIA request], are potential evidence in the FBI's investigation, or may provide leads to or context for potential evidence," Hardy wrote. "As this is an active and ongoing investigation, the FBI is continuing to assess the evidentiary value of any materials retrieved for the investigation from any such server equipment/related devices. Disclosure of evidence, potential evidence, or information that has not yet been assessed for evidentiary value while the investigation is active and ongoing could reasonably be expected to undermine the pending investigation by prematurely revealing its scope and focus."

Hardy noted that the FBI's probe was launched after the bureau received a referral from inspectors general of the State Department and the intelligence community about Clinton's use of a private email server. FBI Director James Comey acknowledged during testimony before the House Judiciary Committee last October that the FBI received a "security referral" from the watchdogs. But beyond that, "the FBI has not and cannot publicly acknowledge the specific focus, scope, or potential targets of any such investigation."

Earlier this month, the Washington Post cited a senior law enforcement official when it reported that the Department of Justice granted immunity to Bryan Pagliano, a former State Department staffer who worked on Clinton's private email server, "as part of a criminal investigation into the possible mishandling of classified information."

"As the FBI looks to wrap up its investigation in the coming months, agents are likely to want to interview Clinton and her senior aides about the decision to use a private server, how it was set up, and whether any of the participants knew they were sending classified information in emails, current and former officials said," according to the Washington Post report.

Clinton's exclusive use of private email to conduct official business was revealed a year ago this month by the New York Times. The State Department released more than 30,000 of Clinton's emails over the course of 10 months under a court order in response to a separate FOIA lawsuit filed by VICE News in January 2015.

More than 1,800 emails were withheld or heavily redacted under exemptions to the FOIA law, including 22 that were not released because they were deemed Top Secret and would cause "exceptionally grave damage" to national security if disclosed. About 65 others were classified Secret and were heavily redacted. VICE News is currently fighting in federal court for a summary of the information contained in those emails.

Clinton has insisted she never sent or received any emails that contained classified information.