US senators warned Thursday of Russias "unprecedented" threat to American and European democratic institutions Thursday as they opened their first public hearing into Moscows interference in the 2016 presidential election.

With the main House probe in political disarray, the Senate Intelligence Committee took the lead investigating how Russia allegedly sought to skew the election in favor of President Donald Trump.

The hearings opened with testimony by academic experts on Russia's history of political meddling, and will include more than 20 witnesses as the committee delves into allegations of collusion with Moscow.

On the witness list are top figures from Trump's election team suspected of communicating with Russian officials during the campaign.

"The American public, indeed, all democratic societies need to understand that malign actors are using old techniques with new platforms to undermine our democratic institutions," said Republican committee chair Richard Burr.

"This is not innuendo or a false allegation. This is not fake news. This is what actually happened to us," said Democratic Senator Mark Warner, the committee’s vice chairman.

Just before the hearing began, Russian President Vladimir Putin again dismissed the US intelligence charge that he masterminded the election disruption effort.

Such charges are "absurd" and "irresponsible," Putin said in the northern city of Arkhangelsk at an international forum on the Arctic.

But US senators warned that Europe is now experiencing the same type of computer hacking and disinformation campaign that the United States did.

"Some of our close allies in Europe are experiencing exactly the same kind of interference in their political processes. Germany has said its parliament has been hacked. French presidential candidates right now have been the subjects of Russian propaganda and disinformation," he added.

The hearing opened amid worries that any inquiry could be stifled by Republicans seeking to protect the White House from the scandal.

Trump has branded the Russia story "fake news" and has said Democrats are trying to undermine the legitimacy of his victory in the November 8 election.

The House Intelligence Committee cancelled planned hearings this week with intelligence and justice officials after the Republican chair, Devin Nunes, said he had new information that Trump aides were "incidentally" picked up in surveillance of foreign agents.

The probe "is about holding Russia to account for this unprecedented attack against our democracy," said Warner.

"I would hope that the president is as anxious as we are to get to the bottom of what happened."

"But I have to say editorially, that the president's recent conduct –- with his wild and uncorroborated accusations about wiretapping, and his inappropriate and unjustified attacks on America's hard-working intelligence professionals –- does give me grave concern."