Democratic presidential candidate Kamala Harris's campaign said Tuesday it had been targeted by foreign hackers, days after rival Donald Trump's campaign suggested that it had been hacked by Iran.

"In July, the campaign legal and security teams were notified by the FBI that we were targeted by a foreign actor influence operation," a Harris campaign official told AFP.

"We have robust cybersecurity measures in place, and are not aware of any security breaches of our systems resulting from those efforts."

The campaign did not give any indication of which foreign power was believed to be behind the attempt but said it remained in contact with law enforcement agencies.

The US State Department warned Iran on Monday of consequences over election interference following the Trump campaign's announcement that it had been hacked.

The Trump campaign suggested on Saturday that Iran was behind the breach in which documents including research they used to vet running mate JD Vance were sent to reporters.

It warned media outlets against reprinting the documents, saying that such action would be "doing the bidding of America's enemies."

The tone was different to 2016, when Trump said at a news conference that he hoped Russia would "find" Hillary Clinton's emails, remarks widely viewed as encouraging further hacks of his election opponent.

US intelligence concluded that Russia intervened in the 2016 election to support Trump, who has rejected the findings.