Trump also said he asked Comey explicitly whether he was personally being investigated as part of the bureau's Russia probe.
"I actually asked him, yes," Trump said. "I said, 'If it's possible, would you let me know am I under investigation?' He said, 'You are not under investigation.'"
At a Senate hearing Thursday, Acting FBI Director Andrew McCabe would not confirm whether Comey did tell Trump that. Such a disclosure would be unusual. McCabe also strongly disputed the White House's assertion that FBI employees had lost confidence in Comey. Just a month ago, Trump publicly expressed his confidence in Comey.
"I know that I'm not under investigation. Me. Personally," the president told NBC News on Thursday. "I'm not talking about campaigns. I'm not talking about anything else."
"I'm not under investigation," he repeated.
White House spokeswoman Sarah Huckabee Sanders said Wednesday that Attorney General Jeff Sessions and Deputy Attorney General Rod Rosenstein came to Trump at a meeting on Monday with concerns about Comey. According to that version of events, Trump then asked Rosenstein to give his recommendation in writing. Sanders claimed that Trump had not decided to fire Comey before asking for the memo and did not make the decision until Tuesday.
Trump has repeatedly denied that his campaign colluded with Russia, and has even suggested that Moscow wasn't responsible for cyberattacks on Democrats.
Russian President Vladimir Putin has said Russia did not meddle in the 2016 election, though the consensus among foreign policy experts in the United States and Europe is that Russian routinely interferes with elections in the West.
Trump met with the Russian ambassador and Russian foreign minister at the White House on Wednesday. The White House said men discussed ISIS and Ukraine.
The U.S. news media was not admitted to that meeting, though a Russian news photographer was there.