"These latest attempts to interfere in US elections are nothing new for the Iranian regime, which, from our vantage point, has undermined democracies -- or attempted to -- for many years now," State Department spokesman Vedant Patel told reporters.

Patel said the United States has raised concerns in the past about Iranian cyber activity.

"We continue to have a number of tools in our tool belt to hold the Iranian regime accountable, and we won't hesitate to use them," Patel said.

He did not confirm whether the United States had assessed that Iran was behind the alleged hacking.

At the White House, National Security Council spokesman John Kirby referred questions on responsibility to the FBI and Justice Department but pointed to an earlier intelligence report that Iran "is working to influence" the presidential election.

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

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

The tone was different than in 2016 when Trump said at a news conference that he hoped Russia would hack rival Hillary Clinton's email to find deleted emails.

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