Donald Trump has dismissed his own intelligence service’s conclusion that Russia interfered in the 2016 presidential election, claiming that Vladimir Putin “was extremely strong and powerful in his denial”.

In an extraordinary press conference between the two leaders in Helsinki, Trump sided with the Russian President over the FBI as he said its probe into the election had been “a disaster”.

In the most jaw-dropping moment, the US President was asked if he trusted US intelligence, which has indicted 12 Russian agents for stealing Democratic Party documents to help him win the vote for Trump. 

Trump said he had been told by his CIA chief that it was Russia which was responsible, but that he saw no reason to believe it.

“I don’t see any reason why it would be”, Trump said. “President Putin was extremely strong and powerful in his denial today.”

Putin, once more, outright rejected any meddling.

At a rambling news conference after a one-on-one meeting with the Russian president, Trump said not a single critical word about Russia on any of the issues that have brought relations between the Washington and Moscow to a post-Cold War low.

Asked if Russia was at all to blame for the poor relations between the two countries, Trump said he holds “both countries responsible”.

“I think the US has been foolish. We’ve all been foolish,” he said, before veering into discussion about his election victory.

“I beat Hillary Clinton easily and frankly we beat her… We won that race and it’s a shame that there can be even a little bit of a cloud over it,” he said.

In response, Putin said he trusted Trump, and Trump trusted him. “Can you name a single fact that would definitively prove collusion?” Putin said.

Trump also said Putin had “an interesting idea” about election interference – but he did not share what the idea was.

Asked if Putin was an adversary, Trump said: “Actually I called him a competitor and a good competitor he is and I think the word competitor is a compliment.”

The President’s repeated warm words for Russia were a marked contrast from the past week when he repeatedly rebuked traditional US allies at a summit of Nato and a visit to Britain.

Underlining the instant fury to Trump siding with Putin, John O Brennan, the CIA director until last year, tweeted: “Donald Trump’s press conference performance in Helsinki rises to & exceeds the threshold of ‘high crimes & misdemeanors’.

“It was nothing short of treasonous. Not only were Trump’s comments imbecilic, he is wholly in the pocket of Putin. Republican Patriots: Where are you???”

The two leaders earlier spent more than two hours in a meeting before they began a working lunch with an expanded group of aides, which also lasted longer than expected.

During the press conference following the summit, the US president said: “We had direct, open, deeply productive dialogue. It went very well.”

He said: “Our relationship has never been worse than it is right now, but that changed as of about four hours ago.

“The disagreements between our two countries are well known, and President Putin and I discussed them at length today.”

Trump said they had spent a great deal of time talking about the Russian interference in the US elections, adding: “I believe this was a message best delivered in person.”

The Russian president, who made a speech first, said there was no reason for any animosity between the two countries and that “the cold war is over”. 

“Today both Russia and the United States face a whole new set of challenges,” he said.

He said the talks had been conducted in “a frank and businesslike atmosphere” and said “I think we can call it a success”.

He added that the negotiations “outlined the first steps” to begin the process of restoring “confidence and trust” between the nations.

The Russian president praised his US counterpart for pursuing dialogue instead of confrontation.

“Hopefully, we now understand each other better. Of course many problems remain, we failed to clear all obstacles.”

He said they favoured “continued cooperation in counterterrorism and cyber security” and that Syria could be an example of successful joint work.

Addressing the fact Trump had asked him about the accusations of meddling in the US elections, he said he had repeated that Russia “has never interfered and will never interfere in internal US affairs”.

As the press waited for the conference to get underway, a man was forcibly removed after reportedly heckling broadcasters and holding up a sign about nuclear weapons. Other members of the press said he was a journalist for The Nation.

Prior to the lunch, Trump told pool reporters that the talks had got off to a “very good start”, according to the US president.

The pair arrived at the Finnish presidential palace within minutes of each other but an hour later than scheduled, in what was widely interpreted as a power play.

After shaking hands for three seconds, the leaders sat down to answer a handful of questions from reporters. 

Putin said it was a pleasure to meet Trump before the US president  congratulated him on the World Cup and on Russia’s performance in the tournament.

“I watched quite a bit of it … it was beautifully done,” he said.

Attending the talks with Trump were US ambassador to Russia Jon Huntsman; US secretary of state, Mike Pompeo; White House chief of staff, John Kelly; national security adviser, John Bolton; Russia expert and Trump adviser, Fiona Hill; and Marina Gross, an interpreter.