Trump and his entourage's possible ties with Russian President Vladimir Putin have been the subject of much speculation.
His tweet came just as the chiefs of the Federal Bureau of Investigation and the National Security Agency were to testify before Congress about ties Trump may have with Russia and his shocking claim that he was wiretapped by his predecessor, Barack Obama.
Former national intelligence director "James Clapper and others stated that there is no evidence Potus colluded with Russia. This story is FAKE NEWS and everyone knows it!" Trump wrote on Twitter.
"The Democrats made up and pushed the Russian story as an excuse for running a terrible campaign. Big advantage in Electoral College & lost!" he added.
FBI Director James Comey and NSA Director Mike Rogers will speak publicly for the first time about two issues that have riveted the American public for weeks and further divided the country's two ever-at-odds political parties.
The stakes for the tycoon-turned-president could hardly be higher.
Comey will appear before the House Intelligence Committee at a hearing probing Russia's interference in the 2016 election campaign. Rogers is also scheduled to testify.
Trump and his entourage's possible ties with Russian President Vladimir Putin have been the subject of much speculation since before he was elected on November 8.
US intelligence agencies in January took the extraordinary step of stating publicly that they believe hackers working for Russia broke into the online accounts of senior Democrats and released embarrassing emails with the aim of helping Trump defeat Hillary Clinton.
Since then, the question of whether Trump and company were, or perhaps still are, in cahoots with Russia has dominated the national conversation.
A congressional panel so far has found no evidence that Trump's campaign colluded with Russia, its chairman said Sunday.
Based on "everything I have up to this morning -- no evidence of collusion," by Trump's team and Moscow, Representative Devin Nunes, chairman of the House Intelligence Committee, told Fox News on Sunday.
Moscow has denied involvement in the hacks, and Trump has denounced the tumult over alleged Russia connections as a "total witch hunt."
Monday's hearing was also expected to address a second explosive issue: Trump's unsubstantiated accusations that the Obama administration wiretapped his phone at Trump Tower in New York during the campaign.
Trump on March 4 tweeted that Obama had "tapped" his phone -- a charge that has consumed political debate in the US capital.