US officials say the Russian president knew about efforts by hackers known as "the Dukes" to infiltrate the Democratic Party's network in a bid to interfere with election results.
How much does the US know about the DNC hack?
US intelligence analysts say the Russian government hacked the Democratic National Committee's (DNC) computer systems to intervene in the 2016 election.
The aim was to help President-elect Donald Trump win the White House as well as undermine the US electoral system.
The DNC contracted cybersecurity firm Crowdstrike to investigate and confirmed the intrusion originated from Russia.
Crowdstrike's investigation found that the adversaries involved engaged "in extensive political and economic espionage for the benefit of the government of the Russian Federation and are believed to be closely linked to the Russian government's powerful and highly capable intelligence services."
The chairman of Clinton's presidential campaign John D. Podesta was also hacked.
Who does the US blame?
A senior White House official said that Russian President Vladimir Putin is directly involved in the cyber attacks, which were designed to impact the US election.
Two senior officials with direct access to the information said with "a high level of confidence" that Putin personally directed how hacked material from Democrats was leaked and used.
"Only Russia's senior-most officials could have authorised these activities," press secretary Josh Earnest said, citing a statement issued by 17 US intelligence agencies in October.
"I don't think things happen in the Russian government of this consequence without Vladimir Putin knowing about it," Ben Rhodes, a top advisor to President Barack Obama, told MSNBC television.
Outgoing president Barack Obama told National Public Radio (NPR) in an interview that the hacking created "more problems for the Clinton campaign than it had for the Trump campaign."
In the NPR interview he said, "there's no doubt that it contributed to an atmosphere in which the only focus for weeks at a time, months at a time were Hillary's emails, the Clinton Foundation, political gossip surrounding the DNC."
However Obama told NPR that the hacking wasn't the main cause of Clinton's loss but it was a driving factor.
"You never know which factors are going to make a difference. But I have no doubt that it had some impact, just based on the coverage," Obama told NPR.
What does Moscow say about this all?
The Kremlin said that Putin has given "a really clear response" to the allegations during the G20 summit in September.
Putin's spokesman Dmitry Peskov said in response to the report that the US should "either stop talking about it or finally produce some evidence, otherwise it all begins to look unseemly."
Did Trump know?
Trump has rejected the reports.
Responding to a question if the intelligence was politicised, Trump answered: "I think so."
"I don't believe they interfered," he said. "It could be Russia. And it could be China. And it could be some guy in his home in New Jersey."
The US president-elect's office has also mocked the CIA. Trump took to Twitter and said:
If Russia, or some other entity, was hacking, why did the White House wait so long to act? Why did they only complain after Hillary lost?— Donald J. Trump (@realDonaldTrump) December 15, 2016
Are we talking about the same cyberattack where it was revealed that head of the DNC illegally gave Hillary the questions to the debate?— Donald J. Trump (@realDonaldTrump) December 16, 2016
Did the hacking affect the election?
As a matter of fact, one month before the election, the US government did formally accuse Russia of cyber attacks against political organisations.
The hacking campaign led to emails of Democrats and Clinton aides being leaked, which at times dominated the election coverage.
The CIA believes the hacked emails were intended to "influence the election" in Trump's favour. They concluded Russia released emails strategically at times with the sole intention of bolstering Trump's campaign.
US officials believe Russia also hacked Republicans but did nothing with the information they found, Reuters reported.