US intelligence officials are "highly confident" Russian President Vladimir Putin "ordered" a campaign to influence the US presidential election.

A new US intelligence report said officials believed "Putin and the Russian government aspired to help" Donald Trump's chances of winning the election when possible by discrediting Hillary Clinton.

Russian intelligence services conducted cyber operations against targets associated with the election, including the Democrats and Republicans, the report said.

It added that Russian intelligence accessed elements of multiple state or local electoral boards, but that the types of systems targeted were not involved in vote tallying.

The report said: "We further assess Putin and the Russian Government developed a clear preference for President-elect Trump.

"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 unfavorably to him."

The report also adds that Russia would seek to use lessons learned from the campaign to "future influence efforts in the United States and worldwide, including against US allies and their election processes".

Earlier, after being briefed by security officials, President-elect Trump said alleged hacking had "absolutely no effect" on the outcome of the election.

He previously said allegations that Russia may have been involved in a bid to sway the election were a "political witch hunt" by people who had lost.

"We need to aggressively combat and stop cyberattacks," he said. "I will appoint a team to give me a plan within 90 days of taking office."

Director of US National Intelligence James Clapper said on Thursday he was "very confident" Moscow hacked Democratic Party institutions and spread fake news during the election campaign, as he gave evidence to the Senate Armed Services Committee.

Senator John McCain, Republican chairman of the committee, said "every American should be alarmed" by Russia's interfering, which was an "unprecedented attack on our democracy".