The United States' top intelligence official has told Congress he was "even more resolute" in his belief that Russia staged cyber attacks on Democrats in the 2016 election campaign, despite scepticism from Republican President-elect Donald Trump about findings on Moscow's role.
James Clapper, the Director of National Intelligence, said on Thursday he had a very high level of confidence that Russia hacked Democratic Party institutions and operatives, as well as disseminating propaganda and fake news aimed at the November 8 election.
"Our assessment now is even more resolute than it was" on October 7 when the government first publicly accused Russia, Clapper told a hearing of the Senate Armed Services Committee.
Although Mr Trump called himself a "big fan" of intelligence agencies, he is heading for a conflict over the issue because he has cast doubt on their assessments that Russia targeted the election. Many lawmakers from both parties are wary of Moscow and distrust Mr Trump's praise of Russian President Vladimir Putin and efforts to heal the rift between the United States and Russia.
Mr Trump will be briefed by intelligence agency chiefs on Friday on hacks that targeted the Democratic Party in the run-up to the election surprisingly won by the New York businessman.
"I don't think we've ever encountered a more aggressive or direct campaign to interfere in our election process than we've seen in this case," said Mr Clapper, who leaves when Mr Trump becomes president on January 20. Mr Clapper stopped short of declaring Russia's actions "an act of war," saying that determination was beyond the scope of his office.
Mr Clapper did not say what made him confident that Russia was behind the cyber attacks, but that conclusion is shared by US intelligence agencies such as the CIA and several private cyber security firms.
Moscow denies the hacking allegations. President Barack Obama last week ordered the expulsion of 35 Russian suspected spies and imposed sanctions on two Russian intelligence agencies he said were involved in hacking US political groups such as the Democratic National Committee (DNC).
In a tweet on Wednesday, Mr Trump cast doubt on a Russian role in the affair, writing: "(WikiLeaks founder) Julian Assange said 'a 14 year old could have hacked Podesta' - why was DNC so careless? Also said the Russians did not give him the info!"
However, on Thursday, Mr Trump said in another post on Twitter that he was not against intelligence agencies or in agreement with Assange, whose organisation leaked Democrats' emails.
Documents stolen from the DNC and candidate Hillary Clinton's campaign chairman John Podesta were leaked to the media before the election, embarrassing the campaign.
US intelligence officials have said Russian cyber attacks were specifically aimed at helping Mr Trump beat Clinton. Several Republicans have acknowledged the Russian hacking but have not linked it to an effort to help Mr Trump win.
Mr Clapper said there were multiple motives for the hacking but pointed out that "they did not change any vote tallies or anything of that sort."