The US Director of National Intelligence James Clapper has said Russia staged cyber attacks to try to interfere in the November 8 presidential election.

A report containing declassified information on the Russian hacking operation would be released next week, Clapper said during an appearance before the Senate Armed Services Committee on Thursday, Efe news reported.

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"We stand more resolutely on that statement than we did on the seventh of October," he said, referring to the intelligence community's earlier assertion that Russia was behind the disclosure by WikiLeaks of e-mails from the Democratic National Committee and from the chairman of Hillary Clinton's presidential campaign, John Podesta.

The content of those e-mails caused some embarrassment to the DNC and to Clinton, who ended up losing the November 8 election to Republican Donald Trump.

The forthcoming report would "ascribe a motivation" to Russian President Vladimir Putin for the ostensible interference in the US election, Clapper said, while declining to offer an opinion on whether the activities had any impact on the outcome of the contest.

Clapper, who would step down when the Obama administration leaves office on January 20, had to apologise to Congress in 2013 after statements he made under oath to the Senate Select Committee on Intelligence turned out to be false.

"Russia is a full-scope cyber actor that poses a major threat to US government, military, diplomatic, commercial and critical infrastructure," according to a joint statement submitted to the committee by Clapper, Marcel Lettre, the under secretary of defense for intelligence; and Adm. Michael S. Rogers, director of the National Security Agency.

In response to a question from the committee, Clapper described the ostensible Russian interference as "multifaceted".

"The hacking was only one part of it. And it also entailed classical propaganda, disinformation, fake news," he said.

President Barack Obama, who last week imposed economic sanctions on several Russian intelligence agencies and private firms and expelled 35 Russian diplomats in reprisal for the alleged electoral interference, is to receive the classified report on the issue later Thursday.

Trump, who has voiced skepticism over the accusations against Moscow, is scheduled to be briefed on the matter Friday by Clapper and the heads of the CIA and FBI.