The secret information on former Secretary of State Hillary Clinton Hillary Diane Rodham ClintonHillicon Valley: FBI chief says Russia is trying to interfere in election to undermine Biden | Treasury Dept. sanctions Iranian government-backed hackers The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters FBI chief says Russia is trying to interfere in election to undermine Biden MORE’s personal email was more highly classified than previously understood, according to the intelligence community’s internal watchdog.

In a letter to Capitol Hill obtained by The Hill, Intelligence Community Inspector General I. Charles McCullough III wrote that Clinton had highly classified information known as “special access programs” (SAP) on her private server.

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“To date, I have received two sworn declarations from one [intelligence community] element,” the watchdog told lawmakers in Congress, Fox reported. “These declarations cover several dozen emails containing classified information determined by the IC element to be at the CONFIDENTIAL, SECRET, and TOP SECRET/SAP levels.

“According to the declarant, these documents contain information derived from classified IC element sources,” he added.

The intelligence office is “coordinating with” the State Department “to determine how these documents should be properly treated in the FOIA [Freedom of Information Act] litigation.”

Details of the letter, which is unclassified, was first reported by Fox News.

The revelation raises the stakes for the types of information in Clinton’s server.

More than 1,300 emails released by the State Department have been classified, though department officials insist that none of the information was classified at the time the emails were sent.

The spy agency watchdog had previously claimed that Clinton also had two emails with “top secret” information on the server.

However, SAP information is above and beyond that, and is used to restrict information on a “need-to-know” basis.

A 2009 executive order signed by President Obama claims that the designation can only be used for when the threat to a program’s information is “exceptional” and the number of people who need access is “reasonably small.”

The watchdog’s finding is likely to further inflame criticism about Clinton’s use of a private email address and personal server, which has dogged her presidential campaign.

Republican National Committee spokesman Michael Short claimed that new revelation “raises serious legal questions,” since she previously signed non-disclosure agreements vowing to protect classified information.

“Hillary Clinton’s decision to skirt government transparency laws with her secret email server has taken on an entirely new level of recklessness,” Short claimed in a statement.

Clinton and the State Department have refused to detail the security precautions taken for the private machine, leaving many to wonder whether her unusual email setup jeopardized sensitive national security and diplomatic information.

State Department spokesman John Kirby declined to address the contents of the letter on Tuesday.

“We are focused on — remain focused on releasing the rest of the remainder of former Secretary Clinton’s emails in manner that protects sensitive information,” he said.

The department is “working very hard” to meet the legal deadline of releasing all 55,000 pages of Clinton’s emails by late this month.

The FBI is currently investigating Clinton’s server for possible mishandling of classified information.