Russian President Vladimir Putin ordered an effort to help Republican Donald Trump's electoral chances by discrediting Democrat Hillary Clinton in the 2016 presidential campaign, U.S. intelligence agencies said in an assessment on Friday.

Russia's objectives were to undermine public faith in the U.S. democratic process, denigrate former secretary of state Clinton, make it harder for her to win and harm her presidency if she did, an unclassified report released by the top U.S. intelligence agency said.

"We assess Russian President Vladimir Putin ordered an influence campaign in 2016 aimed at the U.S. presidential election," the report said. "We further assess Putin and the Russian Government developed a clear preference for President-elect Trump. We have high confidence in these judgements."

The report, although it omitted classified details, was the U.S. government’s starkest public description of what it says was an unprecedented Russian campaign to manipulate the American body politic.

Reports of Russian interference in the already divisive election have roiled Washington, even as the U.S. Congress on Friday certified Trump’s victory in the Electoral College. Clinton won the popular vote by nearly 3 million ballots.

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The report neither assessed "the impact Russian activities had on the outcome of the 2016 election" nor did it provide details on the evidence underpinning its conclusions, a fact likely to keep alive the controversy over what Moscow may have done.

Russia denies the U.S. government's allegations of hacking during the election campaign.

RUSSIAN MILITARY INTELLIGENCE AGENCY

The report said U.S. intelligence agencies believe Russian military intelligence, the GRU, used intermediaries such as WikiLeaks, DCLeaks.com and the Guccifer 2.0 "persona" to release emails that it had acquired from the Democratic National Committee (DNC) and top Democrats as part of the effort.

The release of the emails led to embarrassing media coverage for Clinton and triggered the resignation of the DNC's chief.

WikiLeaks founder Julian Assange has said he did not receive emails stolen from the DNC and top Clinton aide John Podesta from "a state party." However, Assange did not rule out the possibility that he got the material from a third party.

Russian actors were not found to have targeted U.S. systems that are involved in tallying votes, the report said. The report was produced by the Central Intelligence Agency, the Federal Bureau of Investigation and the National Security Agency.

Also on Friday, the U.S. Department of Homeland Security designated U.S. election infrastructure as critical infrastructure, widening the options the government has to protect voting machines from cyber attacks.

While the report found Russia had conducted cyber attacks on both the Democratic and the Republican parties, it made clear that the primary aims were to harm Clinton whether or not she won the election and evolved over time.

"When it appeared to Moscow that Secretary Clinton was likely to win the election, the Russian influence campaign began to focus more on undermining her future presidency," it said.

"We also assess Putin and the Russian Government aspired to help President-elect Trump’s election chances when possible by discrediting Secretary Clinton and publicly contrasting her unfavourably to him," it said. The CIA and FBI had high confidence in this judgement and NSA moderate confidence, the report said.

Neither the Russian embassy in Washington, nor Clinton aides immediately responded to requests for comment.

The report suggested Putin was motivated in part by personal animus toward Clinton.

"Putin most likely wanted to discredit Secretary Clinton because he has publicly blamed her since 2011 for inciting mass protests against his regime in late 2011 and early 2012, and because he holds a grudge for comments he almost certainly saw as disparaging him," it said.

'TROUBLING CHAPTER IN ONGOING STORY'

The report's conclusions, though lacking details of how the Russians may have relayed the material to Wikileaks and others, will give ammunition to Democrats and Trump's fellow Republicans in Congress who want tougher action against Russia, setting the scene for a potential showdown with Trump.

Trump, who has developed a rocky relationship with U.S. spy agencies and at times disparaged their work, defended the legitimacy of his election victory after receiving a nearly two-hour briefing Friday on the report.

In a statement, Trump did not squarely address whether he was told of the agencies' belief Russia carried out the hacking.

Instead, he said: "Russia, China, other countries, outside groups and people are consistently trying to break through the cyber infrastructure of our governmental institutions, businesses and organizations" including the DNC.

"There was absolutely no effect on the outcome of the election including the fact that there was no tampering whatsoever with voting machines," Trump said.

The businessman, who is to be inaugurated as president on Jan. 20, also said he would appoint a team to give him a plan within 90 days of taking office on how to prevent cyber attacks but suggested that he would keep their recommendations secret.

The report did not reveal how the intelligence agencies collected the evidence underpinning their conclusions or the evidence itself, including the means by which Russian military intelligence "relayed" the materials filched from the DNC and other hacking targets to Wikileaks and others, omissions likely to leave the report open to criticism.

Representative Adam Schiff, the top Democrat on the House Permanent Select Committee on Intelligence who was briefed on the report on Friday, took issue with Trump's comments.

"The President-Elect’s statement that the Russian hacking had 'absolutely no effect on the outcome of the election' is not supported by the briefing, report, or common sense," Schiff said.

"It is one thing to say that there was no tampering with vote tallying - which is true - it is another thing to say that the daily dumping of documents disparaging to ... Clinton that was made possible by Russian cyber operations had no effect on the campaigns," he said. "The consequence of these disclosures was hugely beneficial to the President-Elect and damaging to the Clinton campaign, just as the Russians intended."

Senate Intelligence Committee Chairman Richard Burr, a North Carolina Republican, said his panel would continue to compile "facts surrounding Russia's active measures," adding: "This is a troubling chapter in an ongoing story."