Donald Trump and Vladimir Putin have met and shaken hands at Finland's Presidential Palace.
Presidents Donald Trump and Vladimir Putin began a historic summit vowing their determination to forge a reset of troubled relations between the world's greatest nuclear powers.
Trump, bent on forging a personal bond with the Kremlin chief despite allegations of Russian meddling in US politics, went into the summit blaming "stupidity" by his predecessors for plunging ties to their present low.
Looking sombre, the two leaders exchanged a few opening remarks in front of the press at the start of their summit in Helsinki.
Putin, basking in congratulations from Trump and other world leaders for the successful staging of the World Cup in Russia, said: "The time has come to talk in a substantive way about our relations and problem areas of the world."
Before the two leaders went into the first session between just themselves and their interpreters, Trump said the summit would cover "everything from trade to military to missiles to nuclear to China".
"Frankly, we have not been getting along for the last number of years. And I really think the world wants to see us get along. We are the two great nuclear powers," he said.
"I've not been here too long (as president), it's getting close to two years, but we'll be having an extraordinary relationship, I hope so."
'We'll do fine'
Shortly before the summit opened, Trump was asked if he would press Putin over Russia's alleged manipulation of the 2016 election that brought the mercurial property tycoon to power. He said only: "We'll do just fine."
Many US critics had called for the summit's cancellation after new revelations surrounding the alleged election meddling.
But Trump has insisted it is "a good thing to meet", as he attempts to replicate with Putin the sort of personal rapport he proclaims with the autocratic leaders of China and North Korea.
The summit may take the heat out of some of the world's most dangerous conflicts, including Syria.
But there are many points of friction that could yet spoil Trump's hoped-for friendship with the former KGB spymaster.
Trump began the day by firing a Twitter broadside at his domestic opponents, blaming the diplomatic chill on the investigation into alleged Russian election meddling.
"Our relationship with Russia has NEVER been worse thanks to many years of U.S. foolishness and stupidity and now, the Rigged Witch Hunt!" Trump tweeted.
Russia's foreign ministry tweeted in response: "We agree."
Trump's US opponents tried, in turn, to gain traction for the hashtag #BAF (Blame America First).
After a stormy NATO summit in Brussels last week, Trump was accused by critics of cosying up to Putin while undermining the transatlantic alliance.
But over breakfast with Finland's President Sauli Niinisto, he insisted NATO "has never been stronger" and "never been more together" thanks to his insistence on all allies paying their fair share.
Trump, a brash 72-year-old billionaire, has been president for 18 months while Putin, 65, has run Russia for the past 18 years.
In a weekend interview with CBS News, Trump admitted that Russia remains a foe, but he put Moscow on a par with China and the European Union as economic and diplomatic rivals.
The Kremlin has also played down hopes that the odd couple will emerge from their first formal one-on-one summit with a breakthrough.
On Friday Putin's adviser, Yuri Ushakov said: "The state of bilateral relations is very bad... We have to start to set them right."
Indeed, after the bad-tempered NATO summit and a contentious trip by Trump to Britain, anxious European leaders may be relieved if not much comes out of the Helsinki meeting.
Those leaders are already fuming over Trump's imposition of trade tariffs on various countries, including Russia.
Turning the tables, European Union President Donald Tusk said Trump was guilty of "spreading fake news" with his remark about foes, and warned that the trade tensions could spiral into violent "conflict and chaos".
"Europe and China, America and Russia, today in Beijing and in Helsinki, are jointly responsible for improving the world order, not for destroying it," he tweeted.
"I hope this message reaches Helsinki."
Protesters have been on the streets of Helsinki to denounce the policies of both Trump and Putin. Greenpeace draped a giant banner down a church tower urging: "Warm our hearts not our planet."
Giving up ground?
Trump is also under pressure from Britain to press Putin over the nerve agent poisoning of four people in southern England.
One of the victims, Dawn Sturgess, has died and her 19-year-old son Ewan Hope told the Sunday Mirror newspaper: "We need to get justice for my mum."
Many fear that Trump - in his eagerness to prove he was right to seek the summit despite US political opposition - may give up too much ground.
Trump has refused to personally commit to the US refusal to recognise Russia's annexation of Crimea, leaving open the possibility of a climbdown linked to a promise by Putin to somehow rein in Iranian influence in Syria.
If Washington were to acquiesce in Russia's 2014 land-grab, this would break with decades of US policy and send tremors through NATO's exposed eastern flank.
And there will be outrage at home if Trump does not confront Putin over the election scandal.
But the US leader would not say whether he would demand the extradition of 12 Russian intelligence officers who were indicted last week by US special prosecutor Robert Mueller.