US intelligence chiefs said Tuesday that Russian attempts to meddle in US politics are continuing unabated -- and pose a threat to mid-term congressional elections in November.

They also said North Korea's nuclear program poses a potential "existential threat" to the United States, and that the time is nearing for Washington to respond to that danger.

In a Senate Intelligence Committee hearing on the most urgent threats facing the country, Director of National Intelligence Dan Coats and the heads of the CIA, FBI, NSA and two other spy agencies were unanimous in saying that Moscow's efforts to disrupt US politics are as intense now as they were in the 2016 presidential election.

"Throughout the entire community, we have not seen any evidence of any significant change" in Russian behavior, said Coats. "There should be no doubt that Russia perceived its past efforts as successful and sees the 2018 US midterms elections as a potential target for Russian influence operations."

Central Intelligence Agency Director Mike Pompeo said: "We have seen Russian activity and intentions to have an impact on the next election cycle here."

National Security Agency Director Michael Rogers warned that "this is not going to change or stop."

America's leading intelligence agencies concluded last year that Russian President Vladimir Putin had directed a broad intelligence effort to influence the 2016 presidential election to undermine the campaign of Democrat Hillary Clinton and boost Donald Trump's chances.