A threat from Iran prompted moves by the US Secret Service to boost protection around Donald Trump before Saturday's attempted assassination of the former president, which appears unrelated to the original threat, according to two US officials.

Upon learning of the threat, the Biden administration reached out to senior officials at the Secret Service to make them aware, the officials said, adding it was shared with the lead agent on Trump's protection detail and the Trump campaign. That prompted the agency to surge resources and assets to protect Trump. The officials spoke on the condition of anonymity to discuss sensitive intelligence matters.

The additional resources did not prevent Saturday's attack at a Trump rally in Pennsylvania that left Trump injured to the ear, killed one rallygoer and severely injured two more.

“As we have said many times, we have been tracking Iranian threats against former Trump administration officials for years, dating back to the last administration," said National Security Council spokesperson Adrienne Watson. “These threats arise from Iran's desire to seek revenge for the killing of Qassem Soleimani. We consider this a national and homeland security matter of the highest priority.”

Trump ordered the killing of Soleimani, who led the Iranian Islamic Revolutionary Guard Corps's Quds Force, in 2020.

“At this time, law enforcement has reported that their investigation has not identified ties between the shooter and any accomplice or co-conspirator, foreign or domestic,” Watson added.