FBI officials refused to release a pair of emails between investigators and employees at the Department of State, telling a federal judge Monday evening that revealing any details about the correspondence could "compromise" its investigation.

The filing marked the second time the law enforcement agency has sought to keep information about its probe secret in a Freedom of Information Act lawsuit filed by Vice News. The lawsuit is seeking records from Hillary Clinton's private server.

Attorneys for the Justice Department offered to submit "additional details" about the FBI sweep of Clinton's server, but only if the court agreed to keep them under seal.

The FBI has publicly acknowledged its Clinton email probe is a criminal investigation, despite the presumptive Democratic nominee's insistence that it is a routine "security review."