Washington (CNN) President Donald Trump said Thursday he did not ask FBI Director James Comey to end his investigation into Russia's involvement in the 2016 election and possible collusion with the Trump campaign.

Trump emphatically said "no" when asked during a joint news conference with Colombian President Juan Manuel Santos in the White House's East Room.

It was Trump's first time taking questions since his Justice Department named a special counsel to probe Russia's involvement in the 2016 election.

"Well, I respect the move but the entire thing has been a witch hunt," Trump said when asked about the investigation. "There is no collusion between certainly myself and my campaign. But I can always speak for myself and the Russians, zero. I think it divides the country, I think we have a very divided country because of that and many other things. So I can tell you that we want to bring this great country of ours together."

Trump called talk of potential criminal charges or impeachment "totally ridiculous."

He also said he thought that Comey's firing would be bipartisan.

"I think it is totally ridiculous. Everyone thinks so," he said when asked whether he ever thought he did something recently that merited criminal charges or impeachment.

"Director Comey was very unpopular with most people," he said. "I actually thought when I made that decision, and I also got a very, very strong recommendation, as you know, from the Deputy Attorney General Rod Rosenstein. When I made that decision I actually thought it would be a bipartisan decision because you look at all of the people on the Democratic side, not only the Republican side, that were saying such terrible thing about Director Comey."

According to sources familiar with the matter, Trump asked Comey to end the investigation into former national security adviser Michael Flynn, a request documented in a memo written by the former FBI director.

"I hope you can let this go," Comey wrote, quoting Trump in the document, which CNN has not viewed but which was described by the sources.

The bombshell revelation Tuesday escalated the already raging political crises engulfing the White House triggered by the bureau's probe into alleged cooperation between Trump aides and Russia as well as new reports that Trump divulged classified information to top Russian officials.

Trump is both publicly and privately stewing about Rosenstein's decision to name a special counsel. After the White House put out a subdued statement on Wednesday night about former FBI Director Robert Mueller being named special counsel, Trump publicly vented on Thursday morning about the new probe.

"This is the single greatest witch hunt of a politician in American history," he wrote on Twitter. "With all of the illegal acts that took place in the Clinton campaign & Obama Administration, there was never a special counsel appointed!"

This is the single greatest witch hunt of a politician in American history! — Donald J. Trump (@realDonaldTrump) May 18, 2017

With all of the illegal acts that took place in the Clinton campaign & Obama Administration, there was never a special councel appointed! — Donald J. Trump (@realDonaldTrump) May 18, 2017

Trump's tweets signal his White House -- or at least the man in charge -- will try to resist Mueller's investigation, meaning the shadow of that probe will now hang over a White House in need of a morale boost.

Trump has cast himself throughout the Russia investigation as an aggrieved president who is being mistreated by the media.

"No politician in history, and I say this with great surety, has been treated worse or more unfairly," he said on Wednesday to the graduating class of the United States Coast Guard Academy. "You can't let them get you down, you can't let the critics and the naysayers get in the way of your dreams."