Standing side-by-side with Vladimir Putin, United States President Donald Trump has refused to blame the Russian leader for meddling in the 2016 elections, casting doubt on the findings of his own intelligence agencies and sparking a storm of criticism at home.

Key points: Donald Trump's performance denounced as "treasonous" and a "tragic mistake"

Donald Trump's performance denounced as "treasonous" and a "tragic mistake" Vladimir Putin says allegations of election interference "complete nonsense"

Vladimir Putin says allegations of election interference "complete nonsense" US President says Putin is a "competitor" rather than adversary

On a day when he faced pressure from critics, allied countries and even his own staff to take a tough line, Mr Trump said not a single critical word about Moscow on any of the issues that have brought relations between the two powers to the lowest ebb since the Cold War.

Instead, he denounced the "stupidity" of his own country's policy, especially the decision to investigate election interference following the findings of US intelligence agencies.

A prosecutor announced an indictment three days ago of Russian spies for hacking into Democratic Party networks.

Mr Trump's performance at a joint media conference in Helsinki stirred a wave of condemnation in the United States, where the White House has struggled for months to dispel a suggestion that Mr Trump was unwilling to stand up to Mr Putin.

His conduct was denounced as "treasonous" by former CIA chief John Brennan and US senator John McCain called the meeting with Mr Putin a "tragic mistake" and "one of the most disgraceful performances by an American president in memory".

Sorry, this video has expired Vladimir Putin insists his country has no compromising material on Donald Trump (Photo: AP/Pablo Martinez Monsivais)

James Comey, the FBI director fired by Mr Trump, tweeted: "This was the day an American president stood on foreign soil next to a murderous lying thug and refused to back his own country."

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Asked if he believed US intelligence agencies, which concluded that Russia interfered in the 2016 election to help him defeat Democratic candidate Hillary Clinton, Mr Trump said he was not convinced.

"I don't see any reason why it would be [Russia]," Mr Trump said.

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"President Putin was extremely strong and powerful in his denial today."

In one response, the Director of National Intelligence Dan Coats, a Trump nominee approved by Congress, said in a statement:

"We have been clear in our assessments of Russian meddling in the 2016 election and their ongoing, pervasive efforts to undermine our democracy, and we will continue to provide unvarnished and objective intelligence in support of our national security."

Hours after the Helsinki summit, Mr Trump tweeted, "I have GREAT confidence in MY intelligence people."

The US has been foolish: Trump

Sorry, this video has expired Putin says he wanted Trump to win the election (Photo: AP/Pablo Martinez Monsivais)

Before the summit even began, Mr Trump blamed his own country for the deterioration in relations.

"Our relationship with Russia has NEVER been worse thanks to many years of US foolishness and stupidity and now, the Rigged Witch Hunt!" he said on Twitter.

The Russian Foreign Ministry tweeted back: "We agree".

At the news conference, Mr Trump was invited by reporters to offer any criticism of Russia but he repeatedly declined.

Asked if Russia was at all to blame for the poor ties, he said: "I hold 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.

Sorry, this video has expired A look back at Donald Trump and Vladimir Putin's 'relationship'

Mr Trump's 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 during a visit to Britain.

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

Mr Putin spoke of the importance of the two countries working together and praised Mr Trump, at one point interrupting the news conference to give the US President a soccer ball.

Asked whether he had wanted Mr Trump to win the 2016 election and had instructed officials to help him, Mr Putin said "Yes I did", although he denied any interference, saying the allegations were "complete nonsense".

Republican senator Lindsey Graham said Mr Trump's performance would send a message of "weakness" to Moscow.

"Missed opportunity by President Trump to firmly hold Russia accountable for 2016 meddling and deliver a strong warning regarding future elections," Senator Graham said on Twitter.

"This answer by President Trump will be seen by Russia as a sign of weakness and create far more problems than it solves."

Arizona senator Jeff Flake, a frequent Trump critic, said: "I never thought I would see the day when our American President would stand on the stage with the Russian President and place blame on the United States for Russian aggression.

"This is shameful."

Sorry, this video has expired Putin's 'number one enemy' slams Trump meeting

US made to look like a 'pushover'

The Republican head of the US Senate Foreign Relations Committee, Bob Corker, said Mr Trump's comments at the joint media conference made the United States look like a "pushover".

US House of Representatives Speaker Paul Ryan, the top congressional Republican, took a more tempered approach but insisted that Mr Trump "must appreciate that Russia is not our ally".

Former CIA chief Mr Brennan went further, suggesting Mr Trump should be removed from office.

"Donald Trump's press conference performance in Helsinki rises to & exceeds the threshold of 'high crimes & misdemeanors.' It was nothing short of treasonous," he tweeted.

"Not only were Trump's comments imbecilic, he is wholly in the pocket of Putin. Republican Patriots: Where are you???"

Sorry, this video has expired US-Russia relations at 'low point', says diplomat

In some of the strongest words yet reflecting the unease of Washington's traditional allies, Germany's Foreign Minister said on Monday that Europe could no longer rely on the United States.

"To maintain our partnership with the USA we must readjust it," Heiko Maas told the Funke newspaper group.

"The first clear consequence can only be that we need to align ourselves even more closely in Europe."

Reuters/AP