Trump's angry comments followed a New York Times report that the FBI investigated suspicions that Trump might be acting on Russia's behalf after he sacked the bureau's director in 2017.
A separate Washington Post report said that Trump had also aroused concerns by going to unusual lengths to prevent even his close aides from knowing the contents of conversations he had during summits with President Vladimir Putin.
"It's a lot of fake news," Trump said, stressing that he has "those meetings one on one with all leaders." "I have relationships with almost everybody and that's a good thing not a bad thing," he said.
He said that the then-leaders of the FBI who decided to investigate him were "known scoundrels, I guess you could say dirty cops." It is not clear what conclusions the FBI probe reached and what its status might be now.
Trump is also at the center of a huge investigation led by special prosecutor Robert Mueller, who is looking into allegations that the Kremlin worked to influence the 2016 presidential election -- and may have colluded with Trump's campaign.