The US president made the claim, without any supporting evidence, in a tweet following and earlier post describing the special counsel investigation into potential ties between the Trump campaign and Russia, “the greatest witch hunt in American history”.
He tweeted: “Wow, word seems to be coming out that the Obama FBI SPIED ON THE TRUMP CAMPAIGN WITH AN EMBEDDED INFORMANT.”
Quoting a former federal prosecutor he 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!”
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!”