Vladimir Putin personally ordered a campaign that amounted to "propaganda on steroids" as he sought to steal the presidential election from Hillary Clinton, US Senators have claimed.
An army of thousands of "cyber trolls" based in Russia were said to have pumped out "fake news" targeting voters in key states like Wisconsin, Michigan and Pennsylvania, all of which Donald Trump won despite being behind in polls.
Kremlin-backed computer operatives even sought to influence Mr Trump himself, flooding his Twitter feed with conspiracy theories when they knew he was online, the Senate Intelligence Committee was told at its first public hearing in Washington.
Mr Putin, visiting the northern Russian port town of Arkhangelsk, issued his most emphatic denial so far, calling accusations he meddled in the US election "nonsense, endless, and groundless".
He said: "Ronald Reagan was talking about taxes once and said 'Read my lips'...Read my lips - no.". In his denial Mr Putin appeared to have misremembered that it was George H. W. Bush, not Ronald Reagan, who said "Read my lips - no new taxes" at the 1988 Republican Convention.
Democratic Senator Mark Warner, vice-chairman of the Senate committee, said: " "Vladimir Putin ordered a deliberate campaign carefully constructed to undermine our election. There were paid internet trolls working out of a facility in Russia.
"This Russian 'propaganda on steroids' was designed to poison the national conversation in America."
On whether there were links between Russia and Mr Trump's campaign Mr Warner said: "We are seeking to determine whether there is an actual fire, but there is a great, great deal of smoke."
The committee said Russia had pumped out disinformation at "high volume" flooding Twitter and Facebook accounts and using propaganda outlets like Russia Today and Sputnik.
Giving evidence Clint Watts, a former FBI agent, told Senator Marco Rubio, who sits on the committee, that his own presidential campaign had been damaged.
Mr Watts said: "Russia sought to sideline opponents on both sides of the political spectrum. Senator Rubio, in my opinion, you suffered through these efforts."
He added that Russian cyber operatives had been active in US politics after the election, even this week.
Mr Watts said: "This past week we observed social media accounts discrediting Speaker of the House Paul Ryan, hoping to further foment unrest inside US democratic institutions."
When the Russians successfully hacked the emails of the Democratic National Committee in the election they had found a "goldmine" which they were then able to "weaponise" by releasing messages publicly, Mr Watts said.
Mr Putin said he was ready to meet with Mr Trump, and work with him to fight terrorism, and criticised what he called use of the "Russian card" in US politics.
He said: "I don't think it's in the interests of the majority of the American people to bring the US-Russian relations to absurdity for the sake of domestic politics.
"Do we want to completely cut diplomatic relations? Do we want to bring the situation to what it was in the 1960s during the Cuban missile crisis? Where do people behaving in such an irresponsible way want to take us all?"