Iran on Wednesday rejected what it called "malicious" accusations by US media implicating it in a plot to kill former US president Donald Trump.

CNN reported Tuesday that US authorities received intelligence from a "human source" weeks ago on an alleged Iranian plot against the former president, prompting his protection to be boosted. Other US outlets also reported the alleged plot.

CNN said the alleged plot was not linked to Saturday's shooting at a Trump campaign rally in Pennsylvania, in which the former president was wounded and a supporter killed.

The US National Security Council said it had been "tracking Iranian threats against former Trump administration officials for years" after Tehran threatened revenge for the 2020 killing of Revolutionary Guards commander Qasem Soleimani in a US drone strike in neighbouring Iraq.

Iran's mission to the United Nations called the accusations "unsubstantiated and malicious".

Foreign ministry spokesman Nasser Kanani said Iran "strongly rejects any involvement in the recent armed attack against Trump".

He added however that Iran remains "determined to prosecute Trump over his direct role in the assassination of General Qasem Soleimani".

Soleimani headed the foreign operations arm of Iran's Revolutionary Guards, overseeing Iranian military operations across the Middle East.

Trump ordered his killing in a drone strike just outside Baghdad airport.