US accuses Russia of 'pervasive' election meddling
US national security chiefs have lined up to warn American democracy is in the "crosshairs" of foreign adversaries for elections in 2018 and 2020.
Director of National Intelligence Dan Coats said: "We continue to see a pervasive messaging campaign by Russia to weaken and divide the US."
Mr Coats said the efforts were less robust so far than in 2016, and did not appear directed at a single party.
The Kremlin denies US claims it meddled in its last presidential election.
US National Security Adviser John Bolton, FBI Director Chris Wray, National Security Agency Director Paul Nakasone and Homeland Security Secretary Kirstjen Nielsen also spoke at Thursday's White House news conference.
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Mr Coats said Russia was not the only country that was trying to intervene in US elections, without elaborating.
One reporter questioned whether US President Donald Trump had adequately challenged Russian President Vladimir Putin on the matter at their bilateral summit in Finland last month.
Mr Bolton stepped forward to maintain that it had been discussed.
"President Putin said the first issue that President Trump raised was election meddling," the national security adviser told reporters.
Mr Coats was asked if he was accusing rogue Russian individuals or the Kremlin itself of intervening in US elections.
"Both," the intelligence director replied.
He said the hackers were trying to steal information from candidates and government officials and were seeking to influence voters through social media bots.
Mr Coats said: "Our focus here today is simply to tell the American people we acknowledge the threat. It is real."
He added that agencies were meeting weekly to focus on election security ahead of the mid-term elections in November when most of the US Congress faces the voters.
Ms Nielsen said: "Our democracy itself is in the crosshairs.
"Free and fair elections are the cornerstone of our democracy and it has become clear that they have become the target of our adversaries."
President Donald Trump was strongly criticised last month for not condemning alleged Russian actions, while he was in Helsinki.
He has continually called investigations into the matter - and whether his campaign team colluded with Moscow in 2016 - as a witch-hunt.
But the message from the White House on Thursday could not have been clearer.
The FBI director said: "Russia attempted to interfere with the last election and continues to engage in malign influence operations to this day.
"This is a threat that we need to take extremely seriously."
The NSA director said his agency and US Cyber Command were "prepared to conduct operations against those actors attempting to undermine our nation's midterm elections".