The US State Department on Thursday offered a reward of up to 20 million dollars for information on Shahram Poursafi, accusing him of seeking to former US national security adviser John Bolton on behalf of Iran.

"From October 2021 to April 2022, Iran-based Poursafi attempted to hire criminal elements within the United States to murder Mr. Bolton in Washington DC or Maryland in exchange for $300,000," the state department said.

The statement described Poursafi as a uniformed member of the Islamic Revolutionary Guard Corps, Tehran's transnational paramilitary organization dedicated to confronting Israel and the United States.

"Poursafi allegedly provided material support and resources to facilitate the attempted killing. Poursafi told the potential assassin – who actually became a confidential source for U.S. investigators – that once he completed the Bolton murder he would have a second assassination job for him."

The US treasury designated Poursafi a "specially designated global terrorist" in 2023 after the justice department unsealed aspects of the allegations against him the previous year.

The announcement comes days after Donald Trump's campaign said US security agencies had briefed him on threats to the former president's life.

Trump said on Wednesday that the United States should threaten to bomb countries "to smithereens" which seek the assassination of US leaders in the wake of the alleged Iranian plot.