National Intelligence director Dan Coats said there should be no doubt Russia sees the 2018 US midterms as a target.
US intelligence chiefs said on Tuesday 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, Mr Coats said.
"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.
That effort included hacking and releasing emails and documents from the Clinton campaign, filling social media with posts and "news" items aimed at discrediting her, as well as targeting voter-registration operations and election databases.
Mr Trump has repeatedly dismissed the idea that Moscow helped him - and all allegations of collusion - as "fake news," and criticised the intelligence agencies for repeating it.
Countering Russian interference
But a large volume of information has surfaced on Russian use of social media to influence public opinion in US public policy debates.
As a result, leading online media companies like Twitter, Facebook and Google have been forced to begin policing their pages for fake news reports and fake accounts.
"The Russians utilise this tool because it's relatively cheap, it's low risk, it offers what they perceive as plausible deniability, and it is proven to be effective at sowing division," Mr Coats told the Senate panel.
"We expect Russia to continue using propaganda, social media, false-flag personas, sympathetic spokesmen and other means of influence to try to build on its wide range of operations and exacerbate social and political fissures in the United States."
But more than a year after Russian interference became widely known, the intelligence community (IC) chiefs were unable to detail how the United States was countering it or punishing Moscow.
Democratic Senator Jack Reed asked the officials whether Mr Trump had ordered them to take action. But none of the six said the president had specifically done so.
Mr Pompeo said the CIA was acting but could not make the details public.
"We have a significant effort" to rebuff Moscow, he said.
"It is not just our effort, it is a certainly all-of-IC effort. There may be others participating as well, to do our best to push back against this threat."
On North Korea, Mr Coats said its leader Kim Jong-un continues to demonstrate a "provocative nature" and "instability" that makes Pyongyang's nuclear capability more threatening.
"This is an existential threat, potentially to the United States, but also to North Korea," Mr Coats said.
"Kim Jong-un views this as - any kind of a kinetic attack or effort to force him to give up his nuclear weapons - is an existential threat to his nation and to his leadership in particular," he said.
"Our goal is a peaceful settlement," he added.
"We're using maximum pressure on North Korea in various ways."
Separately, Mr Coats stressed the US government's repeated failure to craft a full year's budget, and the large fiscal deficits, constitute another important security threat.
"I'm concerned that our increasing fractious political process, particularly with respect to federal spending, is threatening our ability to properly defend our nation both in the short term and especially in the long term," he said.
The mounting US debt, now over $20 trillion, is "unsustainable and represents a dire threat to our economic and national security".