The United States FBI has claimed Russia and Iran have attempted to influence the US election.
"We have identified that two foreign actors - Iran and Russia - have taken specific actions to influence public opinion relating to our elections," the director of national intelligence John Ratcliffe said in an emergency press conference on Thursday.
"First we have confirmed that some voter registration information has been obtained by Iran and separately by Russia.
"This data can be used by foreign actors to communicate false information to registered voters that they hope will cause confusion, sow chaos and undermine your confidence in American democracy."
He said the FBI has already seen Iran sending "spoof" emails designed to intimidate voters, create social unrest and damage the reputation of US President Donald Trump.
Ratcliffe said they have also seen videos claiming voters can cast fraudulent ballots, including from overseas.
"This video and any claims about such allegedly fraudulent ballots are not true," he said.
"These actions are desperate attempts by desperate adversaries."
Although Russia has not sent out any media, they have obtained some voter information, as they did in the 2016 election.
Ratcliffe called for Americans to "do their part" by not allowing the emails to have any 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," he said.
"We will not tolerate foreign interferance in our election."
FBI Director Chris Wray agreed the FBI would "aggressively investigate" the emails, and Americans should be confident that their votes will count.
Before the press conference, US media had reported Democratic voters had received threatening emails which were originally thought to be from the Proud Boys, a neo-fascist, far-right group.
The emails warned "we will come after you" if the recipients didn't vote for President Donald Trump, ABC reported.
They had been discovered in four battleground states where the votes are spilt between Donald Trump and Joe Biden, including Florida and Alaska.
