Hillary Clinton faced new calls Friday to turn over her personal server after key inspectors general asked the Justice Department to open an investigation into whether classified material was improperly shared on the former secretary of state's account.

In correspondence obtained by Fox News, the inspectors general for the State Department and intelligence community raised deep concerns about the contents of the Democratic presidential candidate's emails. An initial joint memo sent June 29 to State Department Under Secretary for Management Patrick Kennedy said a review of Clinton's email archive showed "hundreds of potentially classified emails."

A memo sent Thursday to lawmakers from the intelligence community's IG repeated the claim, saying emails they reviewed contained classified information even though they weren't marked as such. Office spokeswoman Andrea Williams said they raised concerns with the FBI "that these emails exist on at least one private server and thumb drive with classified information and those are not in the government's possession."

There are conflicting accounts over the nature of the investigation being sought. A source familiar with the probe told Fox News that the watchdogs recommended a criminal investigation into the handling of her email, specifically regarding whether classified information was shared on her personal server.

A Justice Department official confirmed to Fox News that they received a "referral" regarding the "potential compromise of classified information." However, the official said it is not a "criminal referral." Williams also said their office requested a "counterintelligence referral." (A State Department spokesman further clarified that only the intelligence IG referred the case.)

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    In light of the request, though, House Speaker John Boehner and Rep. Trey Gowdy, R-S.C., chairman of the House Benghazi committee, both called for Clinton to turn over her server for an independent evaluation, something she has so far refused to do.

    "Two inspector generals appointed by President Obama have now called on the Justice Department to investigate Secretary Clinton's mishandling of classified email," Boehner said in a statement. "If Secretary Clinton truly has nothing to hide, she can prove it by immediately turning over her server to the proper authorities and allowing them to examine the complete record.

    "... She has claimed she is well-aware of what matters are classified and what are not, and yet she set up a personal email server to discuss matters of national security despite guidance to the contrary from both her State Department and the White House."

    The development poses new challenges for Clinton as she mounts her front-running campaign for the Democratic presidential nomination, amid recent polls showing potential slack in her public support.

    Clinton has repeatedly denied sending or receiving any classified information on her personal account.

    However, the inspectors general wrote in a subsequent memo last week that "several" of Clinton's emails contained classified intelligence information -- and at least one of them was made public. The same memo said the information was not originally marked as classified.

    The findings were first reported by The New York Times.

    Clinton presidential campaign spokesman Nick Merrill issued a statement early Friday denying that Clinton had handled classified materials inappropriately.

    "As has been reported on multiple occasions, any released emails deemed classified by the [Obama] administration have been done so after the fact, and not at the time they were transmitted," Merrill said.

    After the DOJ said the investigation request was not a "criminal" referral, Merrill issued a second statement saying the original Times report referring to a criminal inquiry was "false," and the incident shows "the danger of relying on reckless, inaccurate leaks from partisan sources."

    The Times reported that senior Justice Department officials had not said whether they will open an investigation.

    The existence of Clinton's private email account was first revealed in March of this year. Subsequent reports revealed that the account was run through a personal so-called "homebrew" server based at her New York home. The arrangement has raised questions about Clinton's adherence to federal open records laws and whether she used the account to shield herself from information requests by journalists and government transparency groups.

    Clinton has maintained that she turned over all relevant federal records before deleting her emails off her sever. Amid heavy public criticism, she later asked the State Department to release 55,000 pages of emails she had turned over to them. An initial batch of 3,000 pages was made public June 30.

    The next day, State Department spokesman John Kirby confirmed to Fox News that the department had retroactively deemed about 25 of the Clinton emails to be classified. The Times reported that in May, the State Department also acceded to a request by the FBI to retroactively classify a section of emails related to the 2012 attack on the U.S. consulate in Benghazi, Libya. The Department's decisions don't mean Clinton knowingly sent classified information during her tenure as America's top diplomat.

    The New York Times reports that the inspectors general also criticized the State Department for over-reliance on former Foreign Service officers to determine which information should be classified and failure to consult with the intelligence community on such matters.

    Fox News' Ed Henry and Matthew Dean contributed to this report.