(CNN) Rep. Jerry Nadler says he didn't believe President Donald Trump when he denied reports that FBI Director Christopher Wray had threatened to resign.

"First of all, the President is a known liar, so I don't believe anything he says," Nadler, who is ranking member of the House Judiciary Committee, said on "Erin Burnett Outfront" Tuesday.

"Second of all, the President didn't deny pressuring and urging the FBI to fire the (FBI) Deputy Director, Mr. McCabe, because he didn't approve of his role in the investigation of the President," Nadler told Erin Burnett .

"That is highly improper," he added. "And, again, it's part of a concerted campaign to undermine and to derail an official investigation here."

Trump denied earlier on Tuesday that Wray threatened to resign after Attorney General Jeff Sessions pressured him to make staffing changes among the senior ranks at the FBI.

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