Federal prosecutors will thwart Iran's attempt to undermine US democracy, Attorney General Merrick Garland said in a press conference on Friday, in the wake of indictments against Iranian hackers who allegedly targeted Donald Trump's campaign.

The three defendants remain inside Iran and were acting on behalf of the Islamic Revolutionary Guard Corps, the elite transnational military organization dedicated to confronting Israel and the United States.

"The operation targeted the email accounts of current and former American public officials, journalists and most recently, individuals associated with US political campaigns," Garland said, adding the justice department is dedicated to "countering the threat that Iran poses to our democracy."

"The defendants' own words make clear that they were attempting to undermine former President Trump's campaign in advance of the 2024 US presidential election."

Named as Masoud Jalili, Seyyed Ali Aghamiri and Yasar Balaghi, the men have little chance of being brought before a US court.

Jalili was among seven people targeted in new sanctions on Friday in a separate announcement by the US treasury department for similar allegations of interfering in the upcoming polls.

"Iranian state-sponsored actors undertook a variety of malicious cyber activities, such as hack-and-leak operations and spear-phishing, in an attempt to undermine confidence in the United States’ election" the treasury said.