Updated at 8:30 p.m. ET
In a letter to several Democratic senators Monday, the Justice Department said it "will continue to work closely with the FBI and together, dedicate all necessary resources and take appropriate steps as expeditiously as possible" regarding the review of thousands of newly discovered emails that may be relevant to the investigation of Hillary Clinton's email server.
The letter, signed by Assistant Attorney General Peter Kadzik, came in response to four Senate Democrats who sent the Justice Department a strongly worded letter of their own, pressing for more details about precisely why FBI Director James Comey revived the inquiry into Clinton's emails. That letter was signed by Patrick Leahy of Vermont, the top Democrat on the Judiciary Committee; Dianne Feinstein of California, the top Democrat on the Intelligence Committee; Tom Carper of Delaware, the top Democrat on the Homeland Security Committee; and Ben Cardin of Maryland, the top Democrat on the Foreign Relations Committee.
The letter did not discuss whether the department officials were on board with Comey's decision to disclose the revived investigation last Friday.
Leahy, Feinstein, Carper and Cardin called Comey's disclosure to Congress about the renewed probe "vaguely worded" and left "so many questions unanswered." In particular, they wrote, "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."
The senators had set a deadline of Monday for answers.
The DOJ letter did not include any more information about the investigation.
Republican Chuck Grassley, chairman of the Senate Judiciary Committee and a fierce Clinton critic, sent a letter to Comey Monday, castigating him for not providing "additional context" to his disclosure.
"Without additional context, your disclosure is not fair to Congress, the American people, or Secretary Clinton," Grassley wrote.
Grassley acknowledged DOJ faced a difficult decision about whether to disclose the new development, but said he was disappointed in Comey's cryptic approach.
"While I disagree with those who suggest you should have kept the FBI's discovery secret until after the election, I agree that your disclosure did not go far enough," Grassley wrote. "Unfortunately, your letter failed to give Congress and the American people enough context to evaluate the significance or full meaning of this development."
Grassley then laid out 10 questions for the FBI to answer, including whether the FBI had read the new emails, whether any of the emails are duplicates of those the bureau already investigated and exactly how the FBI learned of the existence of the new emails.
Grassley demanded answers to his questions by Nov. 4.
Also on Monday, the White House carefully tried to steer clear of the political fight over Comey's controversial decision to publicize a new round of scrutiny related to Clinton's private email server.
"I'll neither defend nor criticize what Director Comey has decided to communicate to the public about this investigation," White House spokesman Josh Earnest said Monday.
Comey has become a lightning rod since he notified Congress last Friday that agents had discovered additional emails that could be relevant to the server probe. Although Comey said he couldn't be sure of the emails' significance, the announcement — just a week and a half before the presidential election — sent shock waves through the political world.
Republicans, including Donald Trump, cheered the renewed scrutiny, while Democrats cried foul. The partisan sniping was the opposite of what it had been in July, when Comey concluded a lengthy investigation of Clinton's private server with a finding that no reasonable prosecutor would bring criminal charges.
The new emails were discovered during an unrelated investigation of former Rep. Anthony Weiner, the estranged husband of top Clinton aide Huma Abedin.
Former Attorney General Eric Holder and others have criticized Comey for publicizing the renewed scrutiny at such a preliminary stage, before agents are even aware whether the emails contain additional information.
In an op-ed for the Washington Post, Holder pointed to long-standing Justice Department policies against taking actions near an election that could influence the outcome.
Earnest said he doesn't think that was Comey's intent.
"The president doesn't believe that Director Comey is intentionally trying to influence the outcome of an election," Earnest said. "The president believes that Director Comey is a man of integrity. He's a man of principle. And he's a man of good character."
Obama appointed Comey to lead the FBI. He earlier held high-ranking positions in the George W. Bush administration.
Earnest added that even if there were not an election just over a week away, Justice Department guidelines typically limit what officials are allowed to say about investigations. He suggested that's an important safeguard to protect innocent targets of a probe, given the government's broad powers to gather information.
Officials at the Department of Justice urged Comey not to deliver his notice to Congress but did not order the FBI director to hold off. Doing so might have looked like the department was running interference on behalf of the Democratic presidential candidate.
The White House has also been careful about that, going to what Earnest called "great lengths" to insulate the FBI's probe "from even the appearance of political interference."
As NPR's Carrie Johnson reports, the FBI is currently sifting through the newly discovered emails to figure out whether they are duplicates of what agents already read during the investigation of Clinton that ended in no criminal charges in July. Longtime friends tell Carrie that Comey felt boxed in by the situation — he had testified twice that the server investigation was over. But then he was faced with the new email findings, which he worried could leak.
Clinton has urged the FBI to put out more information, saying over the weekend that "it's pretty strange to put something like that out with such little information right before an election."