Democratic vice presidential nominee Tim KaineTimothy Michael KaineWeek ahead: Crunch time for defense bill’s cyber reforms | Equifax under scrutiny Insurer Anthem to cover bare ObamaCare counties in Virginia Senate votes down Paul's bid to revoke war authorizations MORE said Sunday that FBI Director James Comey's letter to lawmakers regarding the Hillary ClintonHillary Diane Rodham ClintonBiden slams Trump over golf gif hitting Clinton Overnight Cybersecurity: Equifax hit by earlier hack | What to know about Kaspersky controversy | Officials review EU-US privacy pact Overnight Tech: Equifax hit by earlier undisclosed hack | Facebook takes heat over Russian ads | Alt-right Twitter rival may lose domain MORE email server investigation is "unprecedented."

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"I just have no way of understanding these actions. They're a completely unprecedented move," the Virginia senator said during an appearance on ABC's "This Week" with George Stephanopoulos.

"When you haven't even seen the material yourself 11 days before an election, why would you talk about an ongoing investigation?" Kaine asked.

Clinton, the Democratic presidential nominee, made similar comments during a campaign rally in Daytona Beach, Fla., on Saturday.

"In fact, it's not just strange, it's unprecedented and it is deeply troubling," said Clinton.

Following Comey's letter to lawmakers on Friday, The New York Times reported that the emails potentially pertinent to Clinton's server were discovered during a separate FBI investigation into former Rep. Anthony Weiner (D-N.Y.).