President Donald Trump said Russia's Vladimir Putin once again vehemently denied interfering in the 2016 U.S. elections during their discussions on the sidelines of an economic summit Saturday. Trump declined to say whether he believed Putin, but made clear he's not interested in dwelling on the issue.

"He said he absolutely did not meddle in our election. He did not do what they are saying he did," Trump said of Putin, speaking with reporters aboard Air Force One as he travelled to Hanoi, the second-to-last stop of his Asia trip.

"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," Trump said, noting that Putin is "very insulted" by the accusation. Trump called the allegation an "artificial barrier" erected by Democrats -- once again casting doubt on the U.S. intelligence community's conclusion that Russia tried to interfere in the election to help Trump win.

Trump and Putin didn't have a formal meeting while they were in Vietnam for the Asia-Pacific Economic Cooperation summit, but the two spoke informally several times on the event's sidelines and reached an agreement on a number of principles for the future of war-torn Syria.

But Trump made clear that the issue of Russian meddling in the election hovers over the leaders' relationship and said it jeopardized their ability to work together on issues including North Korea's escalating nuclear program and the deadly conflict in Syria.

"Having a good relationship with Russia's a great, great thing. And this artificial Democratic hit job gets in the way," Trump told reporters. "People will die because of it."

Trump danced around the question of whether he believed Putin's denials, telling reporters that pressing the issue would have accomplished little.

"Well, look, I can't stand there and argue with him," Trump said. "I'd rather have him get out of Syria, to be honest with you. I'd rather have him, you know, work with him on the Ukraine than standing and arguing about whether or not -- 'cause that whole thing was set up by the Democrats."

Multiple U.S. intelligence agencies have concluded that Moscow meddled in the 2016 election to try to help Trump win. But Trump called the former heads of those agencies "political hacks" and argued there's plenty of reason to be suspicious of their findings.

Trump's suggestion that he may believe Putin over his own nation's intelligence community is certain to reignite the firestorm over the issue of 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. Congressional committees have also been interviewing campaign and White House staff.

Earlier Saturday, the Kremlin issued a statement saying the leaders had reached agreement on principles for Syria's future now that the Islamic State group has largely been pushed out. Among the agreements' key points, according to the Russians, were an affirmation of de-escalation zones, a system to prevent dangerous incidents between American and Russian forces, and a commitment to a peaceful solution governed by a Geneva peace process.

The Kremlin quickly promoted the agreement as the White House stayed silent. Trump told reporters that the deal was reached "very quickly" and that it would save "tremendous numbers of lives." And he praised his relationship with Putin, saying the two "seem to have a very good feeling for each other and a good relationship, considering we don't know each other well."

Snippets of video from the summit in the seaside city of Danang showed Trump and 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 Trump punctuating his thoughts with hand gestures and Putin smiling.

Journalists travelling with Trump were not granted access to any of the APEC events he participated in Saturday.

White House officials had worked quietly behind the scenes negotiating with the Kremlin on the prospect of a formal meeting. The Russians raised expectations for such a session and Trump told reporters aboard Air Force One en route to Asia that it was "expected we'll meet with Putin" to discuss issues including ramping up pressure on North Korea to halt its nuclear and ballistic weapons program.

As speculation built, the two sides tried to craft the framework of a deal on a path to resolve Syria's civil war once the Islamic State group is defeated that Trump and Putin could announce in a formal bilateral meeting, according to two administration officials not authorized to speak publicly about private discussions and who talked to The Associated Press on condition of anonymity.

But the talks stalled and, minutes before Air Force One touched down in Vietnam, White House press secretary Sarah Huckabee Sanders told reporters the meeting was off.

Trump's visit to Hanoi began with a state diner during which he showered the country with praise, saying it has "truly become one of the great miracles of the world." On Sunday, he'll meet with the country's president and prime minister before heading to his last stop: the Philippines.

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Associated Press writers Laurie Kellman, Darlene Superville and Josh Lederman in Washington contributed to this report.