President Donald Trump said Thursday that he had already decided to fire ousted FBI Director James Comey before Deputy Attorney General Rod Rosenstein wrote up a formal recommendation to do so.

"I was going to fire Comey," Trump told NBC News' Lester Holt in an interview. "Regardless of the recommendation I was going to fire Comey."

The White House initially said Rosenstein's memorandum to Attorney General Jeff Sessions prompted Trump to fire Comey, but Trump contradicted that account, saying he had already planned to do so and requested a memo to back up his decision.

Trump also said that Comey told him "you are not under investigation" during a dinner the two had to discuss Comey's future at the helm of the FBI.

"If it's possible, would you let me know, am I under investigation?" Trump said he asked Comey. "He said, 'you are not under investigation.'"

Trump sharply criticized Comey in the interview as "a showboat" and "a grandstander" and argued that Comey had thrown the FBI into "turmoil."