President Donald Trump's lawyer said he denies ever pressuring former FBI Director James Comey to pledge his personal loyalty or to drop an investigation of his first national security adviser, Michael Flynn, and accused Comey of undermining Trump's administration.

The lawyer, Marc Kasowitz, said Comey had revealed himself as part of a group of people in the government "who are actively attempting to undermine this administration with selective and illegal leaks of classified information and privileged communications," by acknowledging he asked a friend to tell a reporter the contents of a memo he wrote documenting a conversation with Trump.

Comey testified to the Senate Intelligence Committee on Thursday in his first public appearance since Trump fired him on May 9. He said he had documented his conversations with Trump in memos because he was concerned the president would lie about them. He told the panel he asked a friend to release a memo on a meeting in which Trump suggested he drop the Flynn investigation after Trump threatened on Twitter to release "tapes" of their conversations after firing him.