UPDATE - US president confirms he is under FBI investigation

ADDS DETAILS ON COMEY TESTIMONY AND PRIOR DEVELOPMENTS

By Michael Hernandez

WASHINGTON (AA) - U.S. President Donald Trump on Friday confirmed he is being investigated by the FBI for firing ousted Director James Comey.

"I am being investigated for firing the FBI Director by the man who told me to fire the FBI Director!" Trump exclaimed on Twitter, referring to the investigation as a "Witch Hunt".

It appears Trump is referring to Rod Rosenstein, who set the stage for Comey's dismissal in a letter to Trump. But Rosenstein is not currently heading the FBI's probe into the Trump campaign's possible collusion with a Russian campaign that U.S. intelligence officials have said was seeking to tilt the outcome of the 2016 election in Trump's favor.

Rosenstein handed the reigns of that investigation over to independent Special Counsel Robert Mueller about one week after Comey's dismissal.

Reports have been mounting that Mueller is investigating Trump for potential obstruction of justice related to his firing of Comey.

Trump and his White House have offered various explanations for Comey's abrupt ouster, including that he lost the confidence of the bureau's rank and file -- a suggestion flatly dismissed by acting director Andrew McCabe.

During congressional testimony, Comey described the allegations as "lies, plain and simple".

Comey used his his three-hour testimony before the Senate intelligence committee last week to launch a blistering takedown of Trump, calling him a liar no less than five times.

Rosenstein earlier this month confirmed he had the ultimate authority to hire or fire Mueller, but said he has been given a wide berth to conduct the probe.

Citing Rosenstein's private remarks, ABC News reported that he may have to recuse himself from the investigation, potentially following in the footsteps of Attorney General Jeff Sessions who did so in early March in a move that continues to vex the American president.

In a statement many have described as "odd", Rosenstein warned the U.S. public to "exercise caution" before trusting media reports citing anonymous officials, despite the fact that the Trump administration continues to use them in official statements to the media.

In another early morning tweet, Trump said that despite months of investigation no proof has been presented of any collusion he may have had with the Kremlin.

"After 7 months of investigations & committee hearings about my 'collusion with the Russians,' nobody has been able to show any proof. Sad!" he insisted.