FBI Director Chris Wray made clear in a message sent to all bureau employees on Monday night that Deputy Director Andrew McCabe's decision to step aside was a result of forthcoming information to be detailed in an inspector general report, according to a copy of his message obtained by NBC News.

Wray alluded to having seen aspects of the IG's report into the way the FBI handled the investigation into Hillary Clinton's use of a private e-mail server.

"It would be inappropriate for me to comment on specific aspects of the IG's review right now," Wray said in the message. "But I can assure you that I remain staunchly committed to doing this job, in every respect, 'by the book.' I will not be swayed by political or other pressure in my decision making."

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In the next paragraph, Wray explained that McCabe had submitted his intention to retire, suggesting a connection between the findings of the IG report and McCabe's decision.

Several sources familiar with McCabe's move said he made his decision as a result of a meeting with Wray in which the inspector general's investigation was discussed.

News that McCabe would leave seven weeks before he was expected to retire triggered speculation on Monday that he was being forced out under political pressure from President Donald Trump. But several FBI insiders said that was not the case.

FBI Director Christopher Wray testifying on Capitol Hill last month. Aaron P. Bernstein / Reuters

Trump has openly accused McCabe of being biased because his wife took donations from Clinton ally Terry McAuliffe when she ran as a Democrat for a state Senate seat in Virginia. He also fumed at McCabe after James Comey took an FBI plane back to Washington hours after Trump had fired him as the agency's director.

McCabe wrote his own message to the bureau: "It is has been my privilege and honor to work with you all for the past 21 years," he said, adding: "Please always remember that the key to those successes is an unflagging focus on integrity. You are the greatest workforce on earth because you speak up, you tell the truth and you do the right thing. "