HANOI – President Donald Trump said Saturday that Russian President Vladimir Putin again denied his nation tampered in the U.S. presidential election last year when the two men spoke during brief conversations on the sidelines of an international summit.

Trump told reporters that he and Putin had more than one informal discussion after crossing paths at the Asia-Pacific Economic Cooperation forum in Danang, Vietnam, before Trump flew to Hanoi for a bilateral meeting Sunday with Vietnamese leaders.

The conversations mostly centered on the war in Syria, Trump said, but he added that he pressed Putin on Moscow's role in attempting to tamper in the elections.

"He said he didn't meddle," Trump said, answering questions in the press cabin on the Air Force One. "I asked him again. You can only ask so many times . . . He said he absolutely did not meddle in our election. He did not do what they are saying he did."

U.S. intelligence agencies have said Russian hackers stole thousands of emails from the Democratic National Committee and made them public, while also spreading misinformation in an attempt to help Trump beat Democratic presidential nominee Hillary Clinton. Trump, however, has said he does not believe that Russia actively sought to help him.

Congress and a special counsel, former FBI chief Robert S. Mueller III, are heading separate investigations into whether Trump's campaign colluded with Russian agents during the campaign. Mueller's team recently brought indictments against Trump's former campaign chairman, Paul Manafort, and a lower-level campaign aide in connection with that probe.

"There was no collusion," Trump said on the plane. "Everybody knows there was no collusion." The president added that he is determined to enlist Moscow's help to end the civil war in Syria and to ramp up pressure on North Korea over its nuclear weapons program.

He said the investigation into his campaign's ties with Russia could hurt those efforts. "I think it's a shame that something like that could destroy a very important potential relationship between two countries that are really important countries," Trump said. He called a dossier compiled by a former British intelligence agent of alleged ties between Trump and Moscow that was later turned over to U.S. federal law enforcement authorities as "phony." Many of the allegations have not been independently confirmed.

"This is really an artificial barrier that's put in front of us for solving problems with Russia," Trump said. Of Putin, he added: "He says that very strongly, he really seems to be insulted by it and he says he didn't do it. He is very, very strong in the fact that he didn't do it. You have President Putin very strongly, vehemently, says he has nothing to do with that. Now, you are not going to get into an argument, you are going to start talking about Syria and the Ukraine."

Trump also cast blame on President Barack Obama and Clinton, who famously attempted a "reset" of U.S. relations with Russia in Obama's first term. Trump referred to Clinton's "stupid reset button," in which she presented Russian Foreign Minister Sergei Lavrov with an oversized "reset button" that erroneously used the Russian word for "overcharged" instead of "reset."

"Hillary tried it, she failed, nobody mentions it," Trump said. "She hit that reset button, it was a joke. But she tried and she failed." Trump said Obama had bad chemistry with Putin and Clinton was "in way over her head."

Trump did not answer when asked during the flight to Hanoi whether he believed Putin's denial of the tampering.

"Every time he sees me, he says, 'I didn't do that,'" Trump said, "but I really believe that when he tells me that, he means it… I think he's very insulted by it and that's not a good thing for our country."

The Russia investigation is an "artificial Democratic hit job" that "gets in the way," Trump added. "And that's a shame. Because people will die because of it" in Syria and elsewhere. "It's artificially induced and that's shame."

White House aides had said before the APEC summit that Trump had no formal meeting scheduled with Putin, in part because of scheduling conflicts. They acknowledged, however, that it was possible the two leaders might chat if they bumped into one another. Trump and Putin shook hands at an APEC leaders' dinner on Friday and stood next to one another in a "family photo" of the leaders on Saturday.

Trump met with Putin in the summer on the sidelines of the Group of 20 summit in Germany and also spoke extensively at a dinner at that event, a meeting White House officials did not disclose until after it was made public by Ian Bremmer, president of a global risk consulting firm.