The US president promoted the conspiracy theory on Twitter by quoting a right-wing US news organisation's headline, which according to Mr Trump read: "Former CIA analyst Larry Johnson accuses United Kingdom Intelligence of helping Obama Administration Spy on the 2016 Trump Presidential Campaign."
Mr Trump added: "WOW! It is now just a question of time before the truth comes out, and when it does, it will be a beauty!"
The claim, which has been rejected by Britain, does appear to stem from Mr Johnson, a former CIA analyst who is a longtime critic of US intelligence and a defender of Russia.
Mr Johnson has previously falsely claimed the CIA, and not Moscow, may have been behind the hacking of the Democratic National Committee, and has frequently appeared on Russian state media to reject US intelligence conclusions of Russian interference in the 2016 election.
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