Kamala Harris' presidential campaign has confirmed it was warned by the FBI that it was targeted by a foreign influence campaign, sparking renewed fears of meddling in the US election.
The revelation, reported by NBC, came after Donald Trump's campaign claimed it had been hacked in an attempt to distribute election materials.
The FBI has confirmed in a statement that it is investigating foreign hacking efforts against the campaigns. Harris' campaign insisted that its cyber security measures had prevented its systems from being hacked.
"We have robust cybersecurity measures in place and are not aware of any security breaches of our systems resulting from these efforts," the campaign told NBC.
But confirmation of the FBI's warning brought back memories of the 2016 campaign, when Russia was widely believed to have hacked the Democratic party's email system in an effort to destabilize Hillary Clinton's presidential bid and help Trump. Russian hacking efforts included files being given to WikiLeaks, which then released them.
US intelligence officials reported last month that Iran was trying to sow discord and undermine Trump's efforts to retake the White House, although Iranian authorities have denied the allegations.
The renewed suspicions come amid speculation that the country's Islamist regime is preparing an attack on Israel in retaliation for the killing of Ismail Haniyeh, the leader of Hamas, in Tehran last week.