Donald Trump has attacked the decision to appoint a special counsel to investigate possible Russian influence on his election as "the single greatest witch hunt" in US history.
The US president's defiant Twitter remarks were in contrast to his initial reaction to the appointment of former FBI chief Robert Mueller as special counsel to lead the investigation.
Deputy Attorney General Rod Rosenstein appointed Mr Mueller after a succession of events brought to a head questions over Russia's alleged meddling in the election.
They included Mr Trump's firing of FBI Director James Comey, reports that Mr Trump had previously pressured Mr Comey to end a probe of former national security adviser Michael Flynn, and Trump discussing sensitive information on Islamic State with Russia's foreign minister.
On Wednesday, Mr Trump was quoted in a White House statement as saying: "I look forward to this matter concluding quickly."
However he changed his tone in later tweets.
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 counsel appointed!— Donald J. Trump (@realDonaldTrump) May 18, 2017
A number of times previously, Mr Trump has likened the investigation into potential collusion between his campaign and the Russian government to a witch hunt.
On Wednesday, Mr Trump said no politician in history "has been treated worse or more unfairly" than himself.
The announcement of a special counsel apparently took the White House by surprise, with Mr Trump being informed of it only after Deputy Attorney General Rod Rosenstein had signed the order.
The FBI and Congress are looking into potential links between Mr Trump's campaign team and Russia. Mr Mueller will take over the FBI investigation. His appointment has been welcomed by politicians from both sides.
Top House Democrat Nancy Pelosi said an independent commission to investigate the Russia matter was still needed to guard against White House interference. Asked about Mr Trump's tweets, she said the president should "get some thick skin."
Meanwhile, the New York Times reports that former Trump aide Michael Flynn told his transition team at the beginning of January - earlier than was previously thought - that he was under federal investigation for working as a paid lobbyist for Turkey during the election campaign.
Mr Trump appointed Mr Flynn as his national security adviser weeks later despite the warning, but he was sacked after just 24 days.