Trump accuses Obama of embedding spy in his campaign, in angry, misspelled early morning tweet

President brands special counsel investigation 'the greatest witch hunt in American history'

Donald Trump has accused Barack Obama and the FBI of using an "imbedded (sic) informant" to spy on his presidential campaign.

The US president made the claim following an earlier tweet branding the special counsel investigation into potential ties between the Trump campaign and Russia, "the greatest witch hunt in American history".

"Wow, word seems to be coming out that the Obama FBI “SPIED ON THE TRUMP CAMPAIGN WITH AN IMBEDDED INFORMANT,” Mr Trump wrote. He later corrected the misspelling.

(Twitter (Twitter)

Quoting a former federal prosecutor interviewed on Fox News earlier Thursday morning, the president continued: "Andrew McCarthy says, 'There’s probably no doubt that they had at least one confidential informant in the campaign.' If so, this is bigger than Watergate!"

The accusation of FBI spying appears to be a reference to reports in the New York Times that a government informant met "several times" in 2016 with Carter Page and George Papadopolous, former foreign policy advisers to Mr Trump.

Mr Trump's latest outburst comes amid renewed focus on the 71-year-old's presidential campaign, following revelations about a secret FBI interview with an Australian ambassador who met a former Trump campaign aide in 2016.

Of special counsel Robert Mueller's investigation, Mr Trump said: "Congratulations America, we are now into the second year of the greatest Witch Hunt in American History... and there is still No Collusion and No Obstruction.

"The only Collusion was that done by Democrats who were unable to win an Election despite the spending of far more money!"

It was one year ago on Thursday when Mr Mueller, the former FBI director, was appointed to take over the Justice Department's investigation into possible coordination between Russia and Mr Trump's campaign.

The president later branded the investigation a "disgusting, illegal and unwarranted witch hunt", and claimed his administration's first 17 months in office was the most successful in "US history".

"Sorry to the Fake News Media and “Haters,” but that’s the way it is!" he added.

Despite Mr Trump's claims, the 12 months since Mr Mueller was appointed have yielded a flurry of criminal indictments, guilty pleas and tense court appearances.

Hundreds of pages of court filings, and public statements from witnesses, have to an extent pulled back the curtain on an extraordinarily secretive investigation. But much remains hidden from view.

A total of 19 people and three Russian companies have either been indicted or pleaded guilty to criminal charges.

Among those charged are Trump campaign chairman Paul Manafort, who is awaiting trial in Virginia and the District of Columbia, and former White House national security adviser Michael Flynn, who pleaded guilty in December to lying to the FBI and has been cooperating with Mr Mueller's investigation.

Other cooperators include deputy campaign chairman Rick Gates and Mr Papadopoulos, who met an Australian ambassador in London in 2016.

A Dutch lawyer who lied to the FBI is serving a 30-day prison sentence, and a California man who unwittingly sold bank accounts to Russians has also pleaded guilty.

The single largest criminal case involves 13 Russians and three Russian companies, accused of conspiring together to fund a hidden but effective social media campaign to exploit American divisions on race and other hot-button topics as well as favour Mr Trump over Hillary Clinton.

Additional reporting by AP