US national security officials say Iran was responsible for sending threatening emails to Democratic voters.
The emails appeared to come from a far-right pro-Trump group and were meant to “incite unrest”, National Intelligence Director John Ratcliffe said.
Mr Ratcliffe also said US officials found Iran and Russia had obtained “some voter registration information”.
The announcement comes 13 days before the presidential election.
The unusual intelligence briefing this close to the vote is seen as a testament to the government’s concerns over voting interference and disinformation campaigns from foreign actors.
Mr Ratcliffe said Iran’s “spoof emails” claimed to be sent by the far-right Proud Boys group in order to “intimidate voters, incite unrest and damage” President Donald Trump.