WASHINGTON -- Newly released emails show a 2009 request to issue a secure government smartphone to then-Secretary of State Hillary Clinton was denied by the National Security Agency.

The messages made public Wednesday were obtained by Judicial Watch, a conservative legal advocacy group that has filed numerous lawsuits seeking the release of federal documents related to Clinton's tenure as the nation's top diplomat.

The Democratic presidential front-runner has come under intense scrutiny for her decision to use a private email server located in the basement of her New York home to route messages, including some containing sensitive information. Security experts have raised concern the arrangement could have left the messages vulnerable to attack by hackers, including those working for foreign intelligence agencies.

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Clinton's desire for a secure "BlackBerry-like" device, like the one provided to President Barack Obama, is recounted in a series of February 2009 exchanges between high-level officials at the State Department and NSA. Clinton was sworn in as secretary the prior month, and had become "hooked" on reading and answering emails on a BlackBerry she used during the 2008 presidential race.

"We began examining options for (Secretary Clinton) with respect to secure 'BlackBerry-like' communications," wrote Donald R. Reid, the department's assistant director for security infrastructure. "The current state of the art is not too user friendly, has no infrastructure at State, and is very expensive."

Reid wrote that each time they asked the NSA what solution they had worked up to provide a mobile device to Obama, "we were politely told to shut up and color."

Resolving the issue was given such priority as to result in a face-to-face meeting between Clinton chief of staff Cheryl Mills, seven senior State Department staffers with five NSA security experts. According to a summary of the meeting, the request was driven by Clinton's reliance on her BlackBerry for email and keeping track of her calendar. Clinton chose not to use a laptop or desktop computer that could have provided her access to email in her office, according to the summary.

Standard smartphones are not allowed into areas designated as approved for the handling of classified information, such as the block of offices used by senior State Department officials, known by the nickname "Mahogany Row" for the quality of their paneling. Mills said that was inconvenient, because they had to leave their offices and retrieve their phones to check messages.

Mills also asked about waivers provided during the Bush administration to then-Secretary of State Condoleezza Rice for her staff to use BlackBerrys in their secure offices. But the NSA had phased out such waivers due to security concerns.

The department's designated NSA liaison, whose name was redacted from the documents, expressed concerns about security vulnerabilities inherent with using BlackBerry devices for secure communications or in secure areas. However, the specific reasons Clinton's requests were rebuffed are being kept secret by the State Department.

The following month, in March 2009, Clinton began using private email accounts accessed through her BlackBerry to exchange messages with her top aides. The State Department has thus far released more than 52,000 pages of Clinton's work-related emails, a small percentage of which have been withheld because they contain information considered sensitive to national security.

In recent months, Clinton has said her home-based email setup was a mistake, but that she never sent or received anything that was marked classified at the time.

Clinton campaign spokesman Brian Fallon declined to comment Wednesday.

The FBI is investigating whether sensitive information that flowed through Clinton's email server was mishandled. The inspectors general at the State Department and for U.S. intelligence agencies are separately investigating whether rules or laws were broken.

There are currently at least 38 lawsuits, including one filed by The Associated Press, seeking records related to Clinton's service as secretary of state from 2009 to 2013. On Tuesday, Judicial Watch filed a discovery motion in one of those cases seeking to question eight former State Department staffers under oath, including Mills and Reid. The judge overseeing the case indicated last month he was strongly considering allowing lawyers from the group to question Clinton's former aides.

"These documents show that Hillary Clinton knew her BlackBerry wasn't secure," Tom Fitton, the president of Judicial Watch, said Wednesday. "The FBI and prosecutors ought to be very interested in these new materials."

Hillary Clinton racked up resounding victories on Tuesday night in the Democratic primaries.

Clinton's success in at least four of the five contests Tuesday(with Missouri too close to call) helped widen her delegate lead and add to the perception that the Democratic nomination is ultimately hers. Vermont Sen. Bernie Sanders, by contrast, lost the opportunity to have the kind of surprise victory that reinvigorated his candidacy in Michigan last week.