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.
In a Tweet on Sunday, 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, reports BBC.
The US intelligence community has previously concluded that Russia tried to sway the poll in Mr Trump's favour.
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.
"He said he absolutely did not meddle in our election," the US president said.
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".
Mr Trump, who defeated Democratic rival Hillary Clinton, said the allegations were a "Democratic hit job".
In his tweets, he 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?
President Trump has refused to acknowledge a reported assessment by the CIA and other intelligence agencies that Russia was behind the hacking of the Democratic National Committee (DNC) in the run-up to last year's presidential election.
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."