Russia has hit back at claims by the White House that Vladimir Putin was directly involved in cyber attacks designed to influence the outcome of the US election.
"At this point they need to either stop talking about this or finally present some sort of proof," Mr Putin's spokesman, Dmitry Peskov, told journalists during a visit to Japan.
"Otherwise this looks extremely scurrilous."
He was speaking after President Barack Obama said America would respond to the attacks at a "time and place of our choosing".
Whenever a foreign government tried to interfere in US elections, the nation must take action - "and we will", Mr Obama told NPR News.
Barack Obama said the email hacking was more important than the content
"Some of it may be explicit and publicised, some of it may not be," he said. "But Mr Putin is well aware of my feelings about this, because I spoke to him directly about it."
On Thursday the Obama administration suggested President Putin personally authorised the hacking of Democratic officials' email accounts in the run-up to the election and said it was "fact" that such actions helped Donald Trump's campaign.
The information on Mr Putin's alleged involvement reportedly came from spies and diplomatic sources.
Russia has denied state-sponsored hacking to tip the balance towards Mr Trump, who is seen as more pro-Russia than his Democratic rival Hillary Clinton.
Mr Putin's spokesman previously dismissed the latest claims as "laughable nonsense".
In October, the US government formally accused Russia of cyberattacks and President Obama last week ordered a review by intelligence agencies, set to be completed before he leaves office on 20 January.
The Washington Post reported that the CIA believes individuals linked to Moscow fed WikiLeaks emails from Mrs Clinton's campaign chief and the Democratic National Committee.
Those emails were steadily released in the months before the election and damaged Mrs Clinton's campaign.
Mr Trump has called the claims "ridiculous" but Mr Obama's spokesman Josh Earnest said it was "obvious" Mr Trump knew he was being helped by the Russians.
Mr Obama's top adviser, Ben Rhodes, also waded in, telling MSNBC: "I don't think things happen in the Russian government of this consequence without Vladimir Putin knowing about it.
"Everything we know about how Russia operates and how Putin controls that government would suggest that, again, when you're talking about a significant cyber intrusion like this, we're talking about the highest levels of government."
It is the first time officials have publicly pointed the finger at Mr Putin and it will inevitably ramp up tensions between Moscow and President Obama's outgoing administration.Sky News Technology Correspondent Tom Cheshire said hacking was being done by many countries, including the UK, US and China.
He said: "It's part of modern day espionage. We know this has been happening in the UK. GCHQ foiled a cyber attack in the last election.
"The problem is that if the US says how it got the evidence it would reveal where it found it in the network and it gets kicked out. They are going as far as they can and saying, trust us on this, it's Russia. But they may be forced to actually reveal their hand a bit more to put this to rest."