US President Donald Trump will meet his Russian counterpart Vladimir Putin on Monday, ending a tumultuous European tour in which he criticised his allies.
Mr Trump said he had "low expectations" ahead of the talks in the Finnish capital, Helsinki, but added that "maybe some good" would come of them.
The highly anticipated meeting comes after 12 Russians were charged with hacking in the 2016 US elections.
Mr Trump says he will raise the issue, but the summit has no formal agenda.
There have been calls in the US for Mr Trump to cancel the meeting altogether over the indictments, announced on Friday by US Deputy Attorney General Rod Rosenstein.
Russia denies the allegations, and says it is looking forward to the talks as a vehicle for improving relations.
What will be discussed?
US National Security Adviser John Bolton has said 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. Investigators believe the incident is linked to the poisoning of a former Russian spy in March.
Mr Trump elaborated on what will 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."
An uncertain spectacle
By Lyse Doucet, Chief International Correspondent, BBC News, Helsinki
Both leaders will feel they have won simply by meeting with the eyes of the world upon them.
President Putin, still basking in the glory of hosting the World Cup, will project Russian power as he stands shoulder to shoulder with his American counterpart. There is a lot in this for him.
President Trump will again savour the spotlight as the world's self-proclaimed dealmaker. He attacks allies and admires strongmen like the Russian leader.
His penchant for disruptive diplomacy means he could announce unexpected concessions and startle allies and advisors alike.
There could also be some rewards. A dialogue is crucial. Significant issues ranging from a nuclear arms race to wars in Syria and Ukraine deserve their attention.
But with no agenda, little preparation, and a lot of Trumpian unpredictability, no one can be certain what will actually happen.
What are the US hacking allegations?
The 11-count indictment names the Russians defendants, alleging they began cyber-attacks in March 2016 on the email accounts of staff for Hillary Clinton's presidential campaign.
They are accused of using keystroke reading software to spy on the chair of the Democratic National Committee (DNC) and hack into the party's computers.
Top Democrats including party chairman Tom Perez have urged Mr Trump to abandon 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".
What has Mr Trump been doing so far in Europe?
The US president has taken in a Nato summit in Belgium and a visit to the UK ahead of his meeting with Mr Putin. Neither trip 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 Prime Minister Theresa 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.