Threatening emails sent to voters in the US election originated in Iran, the FBI said tonight.
Top intelligence officials, including Director of National Intelligence John Ratcliffe, held a hastily arranged press conference tonight, also announcing some voter registration data had been obtained by Russia and Iran.
And they said a rash of threatening emails sent to Democrat registered voters, apparently from far-right group The Proud Boys, were in fact the work of Iran.
It's unclear whether the registration data was publicly available or hacked - and the officials did not take questions.
They provided no evidence for the claims - but claimed the emails were intended not merely to indimidate voters, but to make Donald Trump look bad.
Director Ratcliffe said: "We have confirmed that some voter registration information has been obtained by Iran, and separately, by Russia.
"We have already seen Iran sending spoofed emails designed to intimidate voters, incite social unrest and damage President Trump."
During the first election TV debate last month, the President was slammed for sending a message to the Proud Boys to "stand back and stand by", when asked to disavow white supremacist groups.
"These actions are desperate attempts by desperate adversaries," Ratcliffe said.
The emails, which warned "you will vote for Trump on Election Day or we will come after you," were sent to thousands of voters in as many as four states in the US.
They told Democrat registered voters The Proud Boys were "in possession of all your information", and told them to change their party affiliation and vote for Trump.
But he insisted the 3 November election is safe and secure.
Speaking at the press conference, Ratcliffe said: "We would like to alert the public that we have identified that two foreign actors, Iran and Russia, have taken specific actions to influence public opinion relating to our elections.
"First, we have confirmed some voter registration information has been obtained by Iran and separately by Russia.
"This data can be used by foreign actors to attempt to communicate false information to registered voters, which they hope will sow confusion, cause chaos and undermine your confidence in American democracy."
He also pointed to a video appearing to show that it was possible to cast fraudulent ballots from overseas.
"This video and any claims about any allegedly fraudulent ballots are not true," he said.
He added: "Even if the adversaries pursue further attempts to intimidate, or attempt to undermine voter confidence, know that our election systems are resilient and you can be confident your votes are secure.
"Although we have not seen the same actions from Russia, we are aware that they have obtained some voter information just as they did in 2016.
"Rest assured that we are prepared for the possibility of actions by those hostile to democracy."
President Trump has repeatedly called the integrity of the election into question, claiming the increased use of postal voting to cope with the Covid-19 pandemic leaves it open to fraud.
There is no evidence that widespread voter fraud exists in the United States, either in person or by mail.