Trump denies asking Comey to drop probe, decries 'witch hunt'

But that changed on Wednesday evening when Rosenstein announced that he had appointed another former FBI director, Robert Mueller, to conduct an independent investigation into Russia's interference in the 2016 campaign.

He added: "The entire thing has been a witch hunt".

With national news swarming over the nomination of a special counsel to investigate possible ties to Russian Federation in Trump's campaign, President Trump is calling it a "witch hunt", denying the claims.

Mr. Trump said he thinks "it's a very, very negative thing".

President Trump however responded early Thursday tweeting "This is the single greatest witch hunt of a politician in American history!"

The revelation by Rosenstein "means that the letter that the president sent us is not accurate", Murphy said, referring to Trump's statement attributing the firing to Rosenstein's memo.

Mr Trump has in vain tried to put investigations into his campaign and his first four months in office behind him. Mr Trump helped launch his political career by claiming - incorrectly - that Mr Obama was not born in the United States, and as president he asserted on Twitter, again with no evidence, that the Obama administration had wiretapped his campaign headquarters.

The White House initially said that letter prompted Trump to fire Comey, but Trump later said he had already chose to dismiss him and was thinking of "this Russian Federation thing".

The Justice Department said Mueller has resigned from his job at a private law firm to take the job of special counsel.

House Speaker Paul Ryan said the appointment was consistent with his goal of ensuring that "thorough and independent investigations are allowed to follow the facts wherever they may lead".

Mueller has been hired to lead the ongoing FBI investigation into Russia's meddling into last year's US Presidential Election and to find out whether some members of the campaign team of Donald Trump were complicit in the whole Russian game that meant to benefit Trump's campaign.

By design, the special counsel will keep their investigation secret, and it could take years to determine if a prosecutable offense has occurred.

In a subsequent statement, Trump said he was confident he would be cleared in the probe. I think it divides the country, I think we have a very divided country because of that and many other things.

On the right, politicians were generally positive about Mueller, though the decision to appoint a special counsel generated mixed feelings, with most prominent Republicans having resisted the idea.

"(Rosenstein) did acknowledge that he learned Comey would be removed prior to him writing his memo", McCaskill said.

Rosenstein can expect to be pressed by lawmakers in both parties about why he made a decision to name a special counsel, which came as a surprise to senior Republicans, including John Cornyn of Texas, the second-ranking GOP senator.

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. "And then on top of that, after the Wednesday performance by Director Comey, you had a person come and have to readjust the record, which many people have never seen before, because there were misstatements made".

Deputy Attorney-General Rod Rosenstein faced questions yesterday by U.S. senators desperate for details about his appointment of a special counsel to investigate possible collusion between President Donald Trump's associates and Russian Federation.

The Senate Intelligence Committee and House Government Oversight Committee have each requested Comey testify before their panels.