REPUBLICAN presidential candidate Donald Trump on Wednesday said Iran may have been behind recent attempts to assassinate him and suggested that if he were president and another country threatened a US presidential candidate, it risked being "blown to smithereens."

Trump made his remarks at a campaign event after US intelligence officials briefed him a day earlier on "real and specific threats from Iran to assassinate him," according to his campaign.

Federal authorities are probing assassination attempts targeting Trump at his Florida golf course in mid-September and at a rally in Pennsylvania in July. There has been no public suggestion by law enforcement agencies of involvement by Iran or any other foreign power in either incident.

"There have been two assassination attempts on my life that we know of, and they may or may not involve, but possibly do, Iran, but I don't really know," Trump said at an event a pipe-fittings plant in Mint Hill, North Carolina.

"We've been threatened very directly by Iran, and I think you have to let them know ... you do any attacks on former presidents or candidates for president, your country gets blown to smithereens," he said.

Trump also questioned why Iran's president, Masoud Pezeshkian, who is attending the United Nations General Assembly in New York, is being protected by US law enforcement.

"We have the president of Iran in our country this week, we have large security forces guarding him, and yet they're threatening our former president and the leading candidate to become the next president — certainly a strange set of circumstances," said Trump, who faces Democrat Kamala Harris, the current vice president, in the Nov 5 election.

Trump's campaign said he would return to Butler, Pennsylvania, the site of the first attempt on his life, for a campaign rally at the same venue on Oct 5.

His stop in North Carolina was Trump's second visit to the state in less than a week, as polls show the race there to be tight. Harris held rallies in two cities there earlier this month.

Republicans in the state are reeling from the allegations that their candidate for governor, Mark Robinson, a top Trump ally, called himself a "Black NAZI" and proposed reviving slavery in anonymous comments posted on a pornography website.

Robinson has denied the allegations and has said he will remain in the governor's race, leaving some Republicans to worry that his candidacy could hurt Trump's chances in the battleground state.

In his remarks on Wednesday, Trump said the FBI has been unable to break into six phones that he said were seized from the man accused of trying to kill Trump on his Florida golf course. Ryan Routh, 58, was charged on Tuesday with attempted assassination of a political candidate.

Trump's claim could not be immediately verified. An FBI spokesperson said it had no comment on an ongoing investigation. The agency has previously said it was able to pull some location data from at least two of Routh's phones. Trump called on Apple to assist the bureau.

US government agencies said last week Iranian hackers sent emails containing stolen material from the Republican former president's campaign to people involved in Democratic President Joe Biden's then re-election campaign, part of an alleged broader effort by Tehran to influence the US election.

Iran has denied US claims of interfering in American affairs. Iran's permanent mission to the United Nations in New York did not respond to a request for comment.

Trump said on Wednesday that the United States' enemies are "desperate" to prevent him from returning to the White House because he will restore the country's standing in the world.

"This is why people in countries want to kill me. They're not happy with me," Trump said. "It's a risky business. This is why they want to kill me. They only kill consequential presidents."

  - Reuters