Donald Trump seemed to confirm for the first time that he was under federal investigation on Twitter on Friday morning.

What does Robert Mueller's team tell us about the Russia investigation? Read more

“I am being investigated for firing the FBI Director by the man who told me to fire the FBI Director! Witch Hunt,” tweeted the president as he both confirmed a blockbuster Washington Post story from Wednesday and contradicted himself yet again about his decision to fire James Comey in May. The Post had reported that Trump was being investigated for potential obstruction of justice by Robert Mueller, the special counsel looking into Russia’s interference in the 2016 presidential election.

“After 7 months of investigations & committee hearings about my ‘collusion with the Russians,’ nobody has been able to show any proof,” Trump also tweeted on Friday. “Sad!” A Washington Post review of recent special counsel and special prosecutor investigations found they took an average of three years to conclude.

The president’s tweets came two years to the day after Trump first launched his improbable presidential bid by famously descending an escalator in Trump Tower in New York, and while his presidency is embroiled in crisis over the federal investigation led by Mueller into his campaign’s ties to Russia.

The inquiry’s apparent expansion to target Trump reportedly focuses on whether the president attempted to obstruct the investigation – in particular, on Trump’s reported attempts to encourage former FBI director James Comey to end an investigation into former national security adviser Michael Flynn. A spokesman for Mueller declined to comment for the Guardian, and a spokesman for Trump’s lawyer did not respond to a request for comment. The White House recently began referring all questions on Trump and Russia to the lawyer Marc Kasowitz.

Comey testified under oath to the Senate intelligence committee earlier in June that Trump told him in a private conversation: “I hope you can see your way clear to letting this go, to letting Flynn go. He is a good guy. I hope you can let this go.”

What would happen if Donald Trump were impeached? Read more

Comey was fired on 9 May, and initially the White House cited his handling of the investigation into Hillary Clinton’s private email server as the reason for his termination, releasing a memo authored by deputy attorney general Rod Rosenstein as a basis for this action. However, several days later, in an interview with NBC News’s Lester Holt, Trump contradicted his administration and cited “this Russia thing” as the reason for Comey’s sacking.

Trump’s tweet comes on the heels of a vague statement on the investigation from Rosenstein, released late on Thursday, and the spate of exclusive stories about the latest developments. “Americans should exercise caution before accepting as true any stories attributed to anonymous ‘officials,’ particularly when they do not identify the country – let alone the branch or agency of government – with which the alleged sources supposedly are affiliated,” said Rosenstein.

He continued: “Americans should be skeptical about anonymous allegations. The Department of Justice has a long-established policy to neither confirm nor deny such allegations.”

Complicating matters further, ABC News reported on Friday that Rosenstein was considering recusing himself from involvement in Mueller’s investigation, handing responsibility for resources, personnel and possible prosecutions to associate attorney general Rachel Brand.

A source close to Trump’s legal team insisted to the Guardian that “the president was not confirming the investigation. He was referring to the Washington Post story from the other night that was based on illegal, anonymous leaks”.

