Moscow (AFP) - The Kremlin on Saturday slammed Washington for its "unprecedented" threats against Moscow over an alleged series of cyber attacks and vowed to respond.

Last week, Washington formally accused the Russian government of trying to "interfere" in the 2016 White House race through cyber attacks on American political institutions.

And on Friday, US Vice President Joe Biden told NBC a "message" would be sent to Russian President Vladimir Putin over the alleged hacking, with the channel saying the CIA was preparing a retaliatory cyber attack "designed to harass and 'embarrass' the Kremlin leadership."

Kremlin spokesman Dmitry Peskov immediately denounced Biden's remarks, saying Moscow would take precautions to safeguard its interests in the face of the increasing "unpredictability and aggressiveness of the United States".

"The threats directed against Moscow and our state's leadership are unprecedented because they are voiced at the level of the US vice president," RIA Novosti news agency quoted him as saying.

"To the backdrop of this aggressive, unpredictable line, we must take measures to protect (our) interests, to hedge risks."

And Kremlin aide Yuri Ushakov vowed Moscow would respond to any US cyber attacks, saying such threats were "borderline insolence", the news agency said.

In the NBC interview, excerpts of which were released late Friday, Biden said Washington would respond "at the time of our choosing and under the circumstances that have the greatest impact."

Earlier this week Russian Foreign Minister Sergei Lavrov shrugged off the US allegations, telling CNN the hacking claims were "flattering" but baseless, with not a "single fact" to prove it.

The Kremlin was propelled to the heart of American politics in July after Hillary Clinton's campaign blamed Russia for an embarrassing leak of emails from the Democratic National Committee.

Russia has been accused of favouring Donald Trump -- who has praised Putin and called for better ties with Moscow -- over the more hawkish Clinton.

Russia's relations with the United States have plunged to their post-Cold War nadir over the conflict in Ukraine and stalled efforts to end the five-year Syrian war.