WASHINGTON, United States (AP) — President Barack Obama is promising that the US will retaliate against Russia for its suspected meddling in America’s election process, an accusation the Kremlin has vehemently denied.

As the White House grew more bullish about suggesting President Vladimir Putin was personally involved, Obama said he’d spoken directly to Putin about his concerns about Russian meddling. He said whenever a foreign government tries to interfere in US elections, the nation must take action “and we will at a time and place of our own choosing”.

“We have been working hard to make sure that what we do is proportional, that what we do is meaningful,” Obama said in an NPR News interview airing Friday.

Obama’s remarks were the clearest indication that whatever response the US is planning, it hasn’t happened yet. The White House has insisted for months that when the US did retaliate, it might not be made public, a position that has created uncertainty about the strength and timing of any response.

Obama was expected to face questions about the hacking and his response during a news conference at the White House on Friday afternoon.

White House officials said it was “fact” that Russian hacking helped Donald Trump’s campaign against Democratic presidential nominee Hillary Clinton. White House press secretary Josh Earnest on Thursday also assailed Trump himself over his refusal to acknowledge the hacking and his attacks on the US intelligence community.

The tough talk from the White House fell flat in Moscow, where Putin spokesman Dmitry Peskov called the accusations baseless and inappropriate.

“They should either stop talking about that, or produce some proof at last,” Peskov told reporters Friday. “Otherwise it all begins to look unseemly.”

There has been no specific, persuasive evidence shared publicly about the extent of Putin’s role or knowledge of the hackings. That lack of proof undercuts Democrats’ strategy to portray Putin’s involvement as irrefutable evidence of a directed Russian government plot to undermine America’s democratic system.

But the White House pointed to a US intelligence assessment released publicly in October that asserted “only Russia’s senior-most officials could have authorised these activities”. And Obama’s deputy national security adviser, Ben Rhodes, connected the dots further, saying Thursday Putin was responsible for the Russian Government’s actions.

“I don’t think things happen in the Russian government of this consequence without Vladimir Putin knowing about it,” he told MSNBC.

Trump struck back Friday morning, with a Twitter post mockingly asking “are we talking about the same cyberattack” in which embarrassing information about the Democratic National Committee was also revealed. His tweet invoked emailed stolen from Hillary Clinton’s campaign chairman and later released publicly in hacking that has been linked to Russia.

In the NPR interview, Obama sough to contrast the current incident with “a traditional understanding that everybody’s trying to gather intelligence on everybody else”.

“One of the things we’re going to have to do over the next decade,” he said, is find an international understanding on rules involving what has become “a new game.” Obama said that US officials should not let “the inter-family argument between Americans” obscure the need for people to “stand together” on this issue.

“My view is that this is not a partisan issue,” the president said, exhorting people to “take it out of election season and move it into governing season”.

The explosive accusation suggests Putin, the leader of perhaps America’s greatest geopolitical foe, as having directly undermined US democracy. US officials have not contended, however, that Trump would have been defeated by Clinton on November 8 if not for Russia’s assistance. Nor has there has been any indication of tampering with the vote-counting.

The dispute over Russia’s role has also fuelled an increasingly public spat between Obama’s White House and Trump’s team that is threatening to spoil the delicate truce that Obama and Trump have forged since Election Day to smooth the billionaire businessman’s move to the White House in little over a month.

Kellyanne Conway, Trump’s senior transition adviser, said it was “breath-taking” and irresponsible that the White House had suggested Trump knew Russia was interfering to help his campaign.

That led Earnest to unload from the White House, arguing that Trump, who has dismissed the CIA’s assessment of Russian interference, should spend less time attacking the intelligence community and more time supporting the investigation that Obama has ordered.

Earnest said it was “obvious” Trump knew what Russia was doing during the campaign, pointing out that Trump had encouraged Moscow during a news conference to find Clinton’s missing emails, repeating the assertion Obama made in “The Daily Show” appearance.

Trump has said he was joking.

“I don’t think anybody at the White House thinks it’s funny that an adversary of the United States engaged in malicious cyber activity to destabilise our democracy,” Earnest said. “That’s not a joke.”