Washington — Amid new revelations about U.S. intelligence information on Hillary Clinton’s private email account, congressional Republicans are demanding to know whether the former secretary of state, her lawyer and the State Department have hindered investigators or compromised classified material.

Clinton was questioned Thursday during a presidential campaign stop about the rapidly widening furor as the State Department revealed her former top aides have been asked to produce their emails for review.

The fallout stems from Clinton’s 2009 decision to route all of her official emails through a private server at her home in Chappaqua, N.Y. — a decision that has roiled the nation’s intelligence community because of concerns that she and her aides may have failed to sufficiently guard secret information.

The latest drama has surrounded Clinton’s attorney, David Kendall.

In a letter dated Wednesday, the chairman of the Senate Homeland Security and Governmental Affairs Committee asked Kendall to explain what he’s done to “safeguard the classified material in (his) possession,” on a computer thumb drive containing 30,400 emails that Clinton turned over to the State Department earlier this year.

“The lax storage and safeguarding of this information could have serious consequences to national security,” wrote Republican Sen. Ron Johnson of Wisconsin, chairman of the panel. McClatchy obtained a copy of the letter.

Johnson demanded that Kendall provide a list of everyone who had access to the thumb drive, identify the manufacturer of the thumb drive and to say which members of the law firm hold security clearances allowing them to possess classified material.

Clinton campaign spokesperson Nick Merrill said Thursday evening, “The thumb drive is secure.”He did not elaborate.

A State Department spokesman, Alec Gerlach, said that the agency had provided Kendall and his law firm “with instructions regarding appropriate measures for physically securing the documents and confirmed via a physical security expert that they are taking those measures.”

But Bradley Moss, a Washington lawyer who handles national security information, said he is perplexed by the arrangement.

“As a general rule, private non-government individuals, even those maintaining a security clearance, are not authorized to privately store classified information,” Moss said.

Kendall, a partner in one of Washington’s elite law firms, Williams and Connelly, declined to respond to phone messages and emails about the thumb drive. The FBI and the Justice Department declined comment on the matter.

Clinton has now drawn scrutiny from Republican leaders of at least five congressional committees for conducting official State Department business on her personal server during her four years in office. McClatchy reported Thursday that information from five intelligence agencies — including the CIA, National Security Agency and Defense Intelligence Agency — was discovered in emails stored on Clinton’s server.

The emails were not marked as classified, and Clinton has insisted that she never sent or received classified information via the private email account.

However, the inspectors general for the State Department and the intelligence community have identified five emails that contained classified information and were not appropriately marked.

The inspectors general found four of the emails containing intelligence secrets in reviewing a sample of just 40 emails, and I. Charles McCullough III, the inspector general for the intelligence community, said State Department officials had warned that there were “potentially hundreds of classified emails” on Clinton’s private server.

Republican Sen. Chuck Grassley of Iowa this week wrote Secretary of State John Kerry that the State Department had “refused” to provide the department’s inspector general with copies of the 30,000 emails and that the department had declined to grant the inspector general for the intelligence community full access on jurisdictional grounds.

“The State Department’s refusal to fully cooperate in this matter is extremely troubling given the risk that national security information is not being adequately protected,” said Grassley, who chairs the Senate Judiciary Committee.

But Gerlach, the State Department spokesman, said a team of about a dozen members of the intelligence community has been granted access to the emails and is “reviewing emails and identifying those that might contain (classified information).”

Gerlach added that “much of what is contained in the former Secretary’s emails does not relate to programs and operations over which the (intelligence inspector general) has oversight responsibilities.”

The State Department inspector general had no immediate comment about access.

Leaders of the Senate Intelligence and Foreign Affairs Committees and the House select committee investigating Sept. 11, 2012 attacks that took the lives of U.S. Ambassador Christopher Stevens and three other Americans in Libya also have pressed for inquiries into Clinton’s handling of her emails.

After a campaign event in Maryland Thursday, Clinton confirmed that several of her State Department aides have been asked to turn over their emails. She did not say which ones, but Gerlach said that Clinton’s communications chief at the State Department, Philippe Reines, had turned over 20 boxes of his emails for review. The department said that all of the aides’ emails would be made public.

Clinton defended the department process for sifting through the emails to protect classified information, though a federal judge overseeing a public records lawsuit this week faulted the agency for taking too long to release emails to the public.

“I think we have been proceeding on a timely fashion,” Clinton said after the campaign event. “The vast majority of the emails that I turned over and that are being turned over are already in the State Department system. This is really a question for the State Department. They are the ones bearing the responsibility to sort through these thousands and thousands of emails.”

In an October 2012 email exchange between Huma Abedin, one of Clinton’s closest confidants and deputy chief of staff, and Stephanie Streett, executive director of the Clinton Foundation, Abedin indicates her “Clinton email” is not working.

Citizens United, a conservative group, obtained the emails through a Freedom of Information Act lawsuit.

At 8:33 a.m. on Oct. 10, 2012, Abedin asks Streett if her email went through.

“My bigger problem right now is that I can’t even get into my clinton email,” she writes.

The exchange clearly indicated Abedin used a separate email than her government email, but does not indicate which one. Judicial Watch, a conservative public interest group that also has sued the State Department seeking communications between Clinton and Abedin, has alleged that Abedin has a “secret account.”

Citizens United, which is led by a man who investigated the Clintons while working on Capitol Hill in the 1990s, said it is more concerned with the national security concerns of Clinton’s system being down.

“This email chain of Hillary Clinton’s closest adviser Huma Abedin raises even more questions about the private Clinton email system and why there must be an independent investigation,” Citizens United President David Bossie said. “How long was the Clinton server down and how often was it down? Was it down as the result of a hack or attempted hack? And, equally important, who serviced the server?

“Hillary Clinton claims she did nothing wrong, but for national security purposes there must be a thorough and impartial investigation to answer these questions.”

McClatchy also has determined some details of the five emails that the intelligence community's inspector general has described as classified and improperly handled.

Intelligence officials who reviewed the five classified emails determined that they included information from five separate intelligence agencies, said a congressional official with knowledge of the matter.

The Benghazi email made public contained information from the National Security Agency, the Defense Intelligence Agency and the National Geospatial-Intelligence Agency, a spy agency that maps and tracks satellite imagery, according to the official, who asked to remain anonymous because of the sensitivity of the matter.

The other four classified emails contained information from the Office of the Director of National Intelligence and the CIA, the official said.

The Office of the Intelligence Community Inspector General did not respond to questions about the matter. The five agencies either referred questions about it to the inspector general's office or declined to comment.