The US Federal Bureau of Investigation has announced that Iran and Russia have taken "specific actions" to influence the 2020 US election.
"First, we have confirmed that some voter registration information has been obtained by Iran, and separately, by Russia," US Director of National Intelligence John Ratcliffe said.
"This data can be used by foreign actors to attempt to communicate false information to registered voters, that they hope will cause confusion and undermine your confidence in American democracy."
Mr Ratcliffe said Iran was distributing video content that implies individuals could cast fraudulent ballots, as well as "spoof emails" that are "designed to intimidate voters".
"We have already seen Iran sending spoofed emails designed to intimidate voters, incite social unrest and damage President Trump," he said.
"These actions are desperate attempts by desperate adversaries."
Mr Ratcliffe and FBI director Chris Wray said the US would impose costs on any foreign countries interfering in the 2020 US election.
He asked "every American" to make sure the interference efforts do not have the intended effect.
"If you receive an intimidating or manipulative email in your inbox, don't be alarmed and do not spread it. This is not a partisan issue," Mr Ratcliffe said.
Mr Wray said Americans should be confident that their vote counts.
"Early unverified claims to the contrary should be viewed with a healthy dose of scepticism," he said,
"We encourage everyone to seek election and voting information from reliable sources.
"Namely, your state election officials, and to be thoughtful, careful, and discerning consumers of information online."
Before the announcement, US media reported that Democratic voters in at least four battleground states, including Florida and Pennsylvania, received threatening emails, falsely purporting to be from the far-right group Proud Boys, that warned "we will come after you" if the recipients didn't vote for President Donald Trump.
More to come.
