Vladimir Putin has again denied meddling in the US presidential election, Donald Trump said after the pair spoke at a summit in Vietnam.
"He says he didn't meddle. I asked him again. You can only ask so many times," Mr Trump told reporters aboard Air Force One on the trip to Hanoi.
"Every time he sees me, he said 'I didn't do that'. And I believe, I really believe that when he tells me that he means it."
Mr Trump and Mr Putin did not have a formal meeting while they were in Vietnam for an economic summit but the two spoke informally several times and reached agreement on a number of principles for the future of war-torn Syria.
But Mr Trump made clear that the issue of Russian meddling in the election hovers over the leaders' relationship - and Mr Putin is "insulted" by the accusation, Mr Trump said.
In a blistering partisan attack, Mr Trump accused Democrats of using the election issue to create a barrier between the US and Russia as the nations work on crises in Syria and Ukraine.
"Having a good relationship with Russia's a great, great thing. And this artificial Democratic hit job gets in the way," Mr Trump told reporters, once again casting doubt on the US intelligence community's conclusion that Russia did try to interfere in the election. "People will die because of it," he said.
Mr Trump's suggestion that he may believe Mr Putin over his own nation's intelligence community is certain to reignite the firestorm over the election meddling.
Meanwhile, a special counsel investigation of potential collusion between Moscow and Trump campaign aides so far has resulted in two indictments for financial and other crimes unrelated to the campaign, as well as a guilty plea.
Mr Trump said the probe into the election hacking was a "fake barrier" placed by Democrats that was hurting the United States' ability to have a relationship with Russia, a distraction that was putting lives at stake.
Snippets of video of conference events from the Asia-Pacific Economic Cooperation conference in Denang have shown Mr Trump and Mr Putin shaking hands and chatting, including during the world leaders' traditional group photo.
The two walked together down a path to the photo site, conversing amiably, with Mr Trump punctuating his thoughts with hand gestures and Mr Putin smiling.
Journalists travelling with Mr Trump were not granted access to any of the Apec events he participated in in the seaside city.