This June 4, 2014, file photo shows Sen. Dianne Feinstein, D-Calif., as she talks to reporters at a news conference at on Capitol Hill in Washington. Associated Press/J. Scott Applewhite Four influential Senate Democrats have formally requested that the FBI provide more details on its renewed investigation into Hillary Clinton's use of a private email server, in a letter sent to FBI Director James Comey and Attorney General Loretta Lynch on Saturday.

Sens. Tom Carper, Patrick Leahy, Dianne Feinstein, and Ben Cardin requested that the FBI give an update no later than Monday detailing what investigative steps are being taken, how many emails are involved, and whether the emails are duplicates of ones that have already been reviewed.

Comey's letter "is troubling because it is vaguely worded and leaves so many questions unanswered," the senators wrote in their letter, which was published in full by The Huffington Post.

They continued: "It is not clear whether the emails identified by the FBI are even in the custody of the FBI, whether any of the emails have already been reviewed, whether Secretary Clinton sent or received them, or whether they even have any significance to the FBI's previous investigation."

Comey has been heavily criticized by both parties for providing few details in his letter on Friday that announced the existence of new emails that appeared to be "pertinent" to the completed investigation in to Clinton's server.

Media reports on Saturday revealed that the FBI still doesn't have a warrant to search the newly discovered emails and apparently has "no idea" of their contents.

The FBI had reportedly discovered the new emails after seizing the laptop of Anthony Weiner, the former congressman and estranged husband of top Clinton aide Huma Abedin. Weiner is under FBI investigation for allegedly sending explicit text messages to a 15-year-old girl.

The senators' letter also blasted the FBI for breaking the "longstanding tradition" of exercising caution with investigations occurring before elections to avoid influencing the outcomes.

"Unfortunately, Director Comey's letter has been misunderstood. It is already being used for political purposes, creating a misleading impression regarding the FBI's intent and actions," the letter said.

It continued: "Just 10 days before a presidential election, the American people deserve more disclosure without delay regarding the FBI's most recent announcement. Anything less would be irresponsible and a disservice to the American people."