The primary "source" of the anti-Trump dossier authored by ex-British intelligence agent Christopher Steele was the subject of an FBI counterintelligence investigation from 2009 to 2011 for suspected contact with Russian intelligence officers, Fox News has learned.

Attorney General Bill Barr penned a letter to Senate Judiciary Committee Chairman Lindsey Graham, R-S.C., on Thursday responding to requests as part of the panel's review into the origins of the Russia probe.

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"In connection with your Committee's investigation of these matters and ongoing hearings, you have been asking us to accelerate this process and to provide any additional information relating to the reliability of the work of Christopher Steele and the so-called 'Steele dossier,' as long as its release would not compromise U.S. Attorney John Durham's ongoing criminal investigation," Barr wrote.

"A footnote in the Inspector General's report contains information, which up till now has been classified and redacted, bearing on the reliability of the Steele dossier," Barr wrote. "The FBI has declassified the relevant portion of the footnote, number 334, which states that 'the Primary Sub-source was the subject of an FBI counterintelligence investigation from 2009 to 2011 that assessed his or her contacts with suspected Russian intelligence officers.'"

Barr added that at his request, the FBI has prepared a declassified summary of certain information from the counterintelligence investigation into the source, which he has shared with the committee.

"I have consulted with Mr. Durham, who originally brought this information to my attention in the course of his investigation, and he has informed me that the disclosure of the information will not interfere with his criminal investigation," Barr wrote, adding that he alerted Director of National Inteligence John Ratcliffe to "certain classified information in possession of the intelligence community" which "bears upon the FBI's knowledge of the reliability of the dossier."

"Mr. Durham confirms that the disclosure of that information would not interfere with his investigaiton, and the Department otherwise defers to the DNI concerning the handling of this information," Barr said.

Durham was appointed by Attorney General Barr last year to investigate the origins of the FBI’s Russia probe shortly after Special Counsel Robert Mueller completed his years-long investigation into whether the campaign colluded with the Russians to influence the 2016 presidential election. Read more at FOX News