A two-year probe into a Moscow-run influence campaign that boosted Trump's candidacy has clouded his presidency since it began, frustrating the Republican president, who has said he seeks better relations with Russia.

Trump and Russian President Vladimir Putin spoke to reporters in Osaka, Japan, on Friday ahead of their first formal face-to-face meeting since a controversial summit in Helsinki last July and the mid-April release of US Special Counsel Robert Mueller's report on Russian election meddling.

Asked by reporters if he would raise the issue during their meeting, held on the sidelines of a Group of 20 summit, Trump said: "Yes, of course I will," drawing a laugh from Putin.

Trump then turned to Putin to give the directive twice, as he wagged a finger at the Russian leader. "Don't meddle in the election, please," Trump said.

Trump's critics have accused him of being too friendly with Putin and castigated him for not publicly confronting the Russian leader in Helsinki after US intelligence agencies concluded that Russian operatives hacked into Democratic Party computers and used fake social media accounts to attack his 2016 opponent, Democrat Hillary Clinton.

His attempt to make light of the situation on Friday prompted a fierce response.

"Russia attacked our democracy in a plot to artificially place Trump into the Oval Office. That is not a laughing matter," House of Representatives Democratic caucus chairman Hakeem Jeffries tweeted.

Michael McFaul, former US ambassador to Russia under Trump's Democratic predecessor Barack Obama, said Trump's deference to Putin was "disappointing but no longer shocking".

Mueller found that Russia meddled in the election, but that there was insufficient evidence that the Trump campaign illegally conspired with Moscow. The Kremlin has denied any meddling.

Putin has said he backed Trump, while Trump has repeatedly dismissed the Mueller probe as a hoax and a witch hunt.

Former US president Jimmy Carter on Friday said a full investigation "would show that Trump didn't actually win the election in 2016.... He was put into office because the Russians interfered on his behalf," according to a report in USA Today.

In Osaka, further attempting to lighten the mood, Trump sought common ground with Putin at the expense of journalists gathered to cover the leaders at the outset of their meeting.

"Get rid of them. 'Fake news' is a great term, isn't it? You don't have this problem in Russia but we do," Trump said.

To which Putin responded, in English: "We also have. It's the same."

The joke drew harsh rebukes stateside, where journalists were noting the one-year anniversary of the deaths of five US journalists at a Maryland newspaper.

US-Russia relations have been sour for years, worsening after Russia annexed Crimea from Ukraine in 2014 and backed Syrian President Bashar al-Assad in the Syrian war. In a recent television interview, Putin said that relations were "getting worse and worse".

Trump has sought to turn the page and work with Putin on issues such as reining in North Korea's nuclear ambitions.

On Friday, Trump called it "a great honour" to meet with his Russian counterpart.

The two were scheduled to meet at the last G20 in November, but Trump cancelled, citing Russia's seizure of Ukrainian navy ships and sailors. The two spoke informally at the event and at a lunch in Paris earlier that month. In May, they had their first extensive phone conversation in months.

"We've had great meetings. We've had a very, very good relationship," Trump said on Friday. "And we look forward to spending some very good time together."

Democrats chided Trump for not being more forceful with Putin ahead of the November 2020 US presidential election, in which Trump is seeking a second term.

"Russian interference in our democracy should concern every American," tweeted US House Intelligence Committee chairman Adam Schiff, a Democrat. "If we don't act to secure 2020 against further interference, Putin will have the last laugh."

Australian Associated Press