US President Donald Trump said he had "good discussions" with Russian leader Vladimir Putin when they met briefly at an Asia-Pacific summit in Vietnam.
On Twitter, he blasted "haters and fools", who, he said, do not encourage good relations between the countries.
Earlier he said Mr Putin told him he was insulted by allegations of Russian interference in the 2016 US election.
The US intelligence community has previously concluded that Russia tried to sway the poll in Mr Trump's favour.
"He said he absolutely did not meddle in our election," the US president said.
However, after intense criticism, Mr Trump clarified that he supported US intelligence agencies in their conclusion. "As to whether or not I believe it or not, I'm with our agencies. I believe in our... intelligence agencies," he said.
"What he believes, he believes," he added, of Mr Putin's belief that Russia did not meddle.
The two leaders had no formal bilateral talks during the Asia-Pacific Economic Co-operation (Apec) event, but meet in passing on three occasions. They spoke about the Syria crisis and the election allegations, according to Mr Trump.
Republican Senator John McCain, a vehement critic of Mr Trump, called him naive for "taking the word of a KGB colonel over that of the American intelligence community".
A CIA statement passed to US media said: "The intelligence assessment with regard to Russian election meddling has not changed."
When will all the haters and fools out there realize that having a good relationship with Russia is a good thing, not a bad thing. There always playing politics - bad for our country. I want to solve North Korea, Syria, Ukraine, terrorism, and Russia can greatly help!— Donald J. Trump (@realDonaldTrump) November 12, 2017
In his tweets, Mr Trump also said his predecessor, Barack Obama lacked "chemistry" with President Putin.
The US justice department has appointed special investigator Robert Mueller to examine any possible collusion involving Mr Trump's team, and legal action has already been taken against several former aides.
What are the allegations against Russia?
The contents of the emails, passed to Wikileaks and posted online, were embarrassing to the Democrats and shook up the presidential campaign, which ended in defeat for Hillary Clinton.
In addition to the Mueller inquiry, congressional committees have been set up to carry out their own investigations.
Relations between the US and Russia have been strained for years, with the Kremlin long accusing Washington of seeking to sway elections in Russia and other ex-Soviet states including Ukraine and Georgia.
While Russian hackers are widely suspected of involvement, there has been no conclusive link to the Kremlin.
Denying that Russia had tried to interfere last year by fostering contacts with Mr Trump's campaign, Mr Putin told reporters in Vietnam: "Everything about the so-called Russian dossier in the US is a manifestation of a continuing domestic political struggle."
What does Mr Trump say to the allegations?
He said he believed Mr Putin had been "very insulted by" the allegations and that was "not a good thing" for America.
"He [Putin] said he didn't meddle," he added. "I asked him again."
Asked if he believed Mr Putin, he replied, "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 out on a limb again
Aleem Maqbool, BBC News, Da Nang
Donald Trump once again goes against the findings of his own intelligence agencies.
Because although the US justice department is investigating the scale and nature of Russian interference in the election of 2016 (and any links to the Trump campaign), the American intelligence community has already long determined that Russia did, indeed, interfere.
Yet Mr Trump suggested this story was not only entirely fabricated by his political opponents, it might even be costing lives in Syria, because it is getting in the way of his relationship with the Russian president and hampering their ability to help solve the conflict together.
"People will die because of it, and it's a pure hit job, and it's artificially induced and that's a shame," he said.
It is hard to know what the president hopes to achieve with this type of rhetoric. The investigation goes on.
How did the two presidents get on in Vietnam?
Mr Trump and Mr Putin met for the first time in July at a G20 summit in the German city of Hamburg. In Da Nang they were seen chatting briefly on three occasions within 24 hours during the Asia-Pacific Economic Co-operation (Apec) summit.
However, they had no formal bilateral meeting, with Mr Putin blaming it on scheduling and protocol.
They had warm words for each other, with the US president talking of their mutual "very good feeling" and the Russian leader describing his counterpart as "well-mannered... and comfortable to deal with".
They did manage to sign off a statement vowing to continue the battle against so-called Islamic State in Syria until the militants are defeated and calling for a political solution to the conflict.
How far has US justice department investigation progressed?
He testified that Russian nationals had contacted him in an attempt to gain influence with the Trump campaign, offering "dirt" in the form of "thousands of emails" on Mrs Clinton in April 2016 - two months before the DNC emails were leaked.
On Saturday, Mr Putin brushed aside US media reports that a woman wrongly identified by Mr Papadopoulos as the Russian president's niece had offered to help broker meetings with Kremlin officials.
"I do not know anything about it and I think it is just some fantasies," Mr Putin said.
Mr Trump's former campaign manager, Paul Manafort, and an associate were also placed under house arrest on charges of money laundering as a result of the Mueller inquiry, but the charges do not relate to the election.