Key former Trump aides are under US investigation for possible collaboration with the Kremlin and the issue of whether Moscow interfered with last year's vote has overshadowed the tail end of the president's ongoing Asia tour.
Trump returned to the subject in an early morning Twitter storm, which also saw him take a sarcastic dig at North Korea's "short and fat" leader Kim Jong-Un.
"I believe he feels he and Russia did not meddle in the election," Trump said.
"As to whether or not I believe it or not, I'm with our agencies. I believe in our... intelligence agencies," he added.
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In May, US intelligence chiefs told Congress they agreed with their analysts' conclusion that Russia had interfered in the election.
CIA director Mike Pompeo, who was appointed by Trump, said he still believed in that evaluation in a statement to CNN Saturday.
"There (sic) always playing politics - bad for our country. I want to solve North Korea, Syria, Ukraine, terrorism, and Russia can greatly help!" he said.
Trump was in Hanoi for a brisk visit with Vietnam's top communist leaders to drum up trade deals and seek further support on containing North Korea's nuclear weapons ambitions, which have been a dominant theme on each leg of his Asia tour.
Citing descriptions by North Korean officials and state media of him as an "old" man, another Trump tweet suggested he was disappointed by what he took to be a personal attack from the North's young leader.
"Oh well, I try so hard to be his friend - and maybe someday that will happen!" he added.
Later at the press conference, he insisted he hadn't been joking about eventually befriending a man he denounced just last week as a "twisted" dictator.
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