US President Donald Trump has said getting on with Russia is “a good thing, not a bad thing” at the start of his first summit with Vladimir Putin.
Mr Trump said he hoped for an “extraordinary relationship” as the two presidents met in Helsinki, Finland.
Earlier Mr Trump denounced his predecessors’ “stupidity” for tensions.
US-Russia relations have been strained by Moscow’s annexation of Crimea in 2014 and by claims that the Kremlin helped Mr Trump win the 2016 election.
Some US politicians had called for the summit to be cancelled after 12 Russian military intelligence agents were charged on Friday with hacking the presidential campaign of Democratic candidate Hillary Clinton.
But in his tweet, Mr Trump put the blame for the deterioration in relations with Russia on “years of US foolishness and stupidity and now, the Rigged Witch Hunt”.
BBC diplomatic correspondent James Robbins says Mr Trump’s tweet is likely to alarm White House advisers, already nervous about the risks of giving too much ground to the Russian leader during the talks.
Many in the West have criticised Moscow for what they regard as its destabilising activities in Ukraine. The US, among others, has imposed sanctions on Russia over its annexation of Crimea.
The summit – in which the two leaders are being joined only by their interpreters – comes after a tumultuous European tour that saw Mr Trump criticise allies of the US over trade and military spending.
What are the main sources of tension with Russia?
Russia has been criticised in the US because of its military support for President Bashar al-Assad in Syria as well as its actions in Ukraine.
Tensions also are high as a result of accusations of Russian interference in the 2016 US election. The allegations are being investigated by Special Counsel Robert Mueller.
Mr Trump has consistently denounced the inquiry as a “witch hunt”.
The 12 Russians indicted on Friday were targeted as part of Mr Mueller’s investigation.
Top Democrats including party chairman Tom Perez have urged Mr Trump to cancel the talks, saying Mr Putin was “not a friend of the United States”.
On the Republican side, Senator John McCain said the summit “should not move forward” unless the president “is prepared to hold Putin accountable”.
Russia denies the hacking allegations, and says it is looking forward to the talks as a vehicle for improving relations.
What is being discussed at the summit?
US National Security Adviser John Bolton has said that both sides have agreed the meeting will have no set agenda.
But he said he found it “hard to believe” Mr Putin did not know about the alleged election hacking and the subject would be mentioned.
“That’s what one of the purposes of this meeting is, so the president can see eye to eye with President Putin and ask him about it,” he told ABC News.
Mr Trump has also been urged to raise the poisoning of two people in the UK who came into contact with the nerve agent Novichok on 30 June. Investigators believe the incident is linked to the poisoning of a former Russian spy and his daughter in March.
Mr Trump elaborated on what would be discussed at the summit during a joint press conference with UK Prime Minister Theresa May last week.
“We’ll be talking about Syria,” he said. “We’ll be talking about other parts of the Middle East. I will be talking about nuclear proliferation.”
This is not the first time US and Russian leaders have met in Helsinki.
Finland remained politically and militarily neutral after World War Two, as US and Soviet Union went headlong into the Cold War, making it an attractive meeting spot for the two superpowers.
The city saw the signing of the 1975 Helsinki Accords, which are credited for improving relations between the Soviet Union and Western countries.
Helsinki remained a destination in the post-Soviet era, and the Trump-Putin summit is the fourth such meeting in the city.
What has Mr Trump been doing so far in Europe?
His tour has included a Nato summit in Belgium and a visit to the UK. Neither passed without controversy.
Following the Nato summit, Mr Trump said the allies had pledged to “substantially” raise their defence budgets but other leaders cast doubt on this claim.
The UK visit also had its ups and downs after Mr Trump told a newspaper the US would probably not give the UK a trade deal under the terms of Mrs May’s Brexit plans – and then later appeared to backtrack on this position.
He also said Europe was “losing its character” because of immigration from Africa and the Middle East.
On Sunday, just before he departed for Helsinki, Mr Trump described the European Union as a foe on trade.
He told CBS News that European countries were taking advantage of the US and not paying their Nato bills.
Trump-Putin summit: US seeks better ties with Russia