Trump: 'Phony and fraudulent' Russia probe 'should never' happen again

In a tweet on Sunday, Trump also said that such a probe "should never" be able to happen to another president.

Since May 2017, US Special Counsel Robert Mueller, a former FBI director, had been examining whether Trump’s election campaign colluded with Moscow to try to influence the 2016 election and whether the Republican president later unlawfully tried to obstruct his investigation.

US intelligence agencies claimed Moscow had meddled in the election with a campaign of email hacking and online propaganda aimed at sowing discord in the United States, hurting Democratic candidate Hillary Clinton and helping Trump.

Both Trump and Russia, however, have repeatedly denied the accusations. Trump has sought to discredit the investigation, calling it a “witch hunt” and accusing Mueller of conflicts of interest.

On Friday, the US president launched harsh attacks on Democratic lawmakers and the media after Mueller’s investigation found no evidence of collusion between the Trump campaign and Russia ahead of the 2016 election.

Attorney General William Barr, a Trump appointee, said in a four-page summary of Mueller's main findings released last week that the special counsel's team had concluded that no one in Trump’s campaign “conspired or coordinated with the Russian government.”

Trump had previously said that an investigation similar to the Russia probe should never happen again to another president.

"This should never happen to a president again. We can’t allow that to take place," he said last week.

Meanwhile, Republicans in Congress have called for investigations into the origins of the Russia probe and asserted that the results invalidate the necessity of the investigation.