Washington: US President Donald Trump warned on Sunday that any prospective successor to Iran's slain supreme leader would face a short-lived tenure without the explicit endorsement of the United States.

In an interview with ABC News, the president asserted that Washington must have a decisive role in the selection of the next Iranian head of state to prevent a recurrence of the current military conflict.

"He's going to have to get approval from us," Trump said. "If he doesn't get approval from us, he's not going to last long."

The president framed his demand as a strategic necessity, telling the network that he intends to ensure the United States does not "have to go back in five years and have to do the same thing again or worse let them have a nuclear weapon."

The ultimatum arrived as Iran’s Assembly of Experts, the clerical body tasked with naming a successor to Ayatollah Ali Khamenei, who was killed in the opening wave of U.S.-Israeli strikes on Feb. 28, reportedly finalised its vote. While a formal announcement has been delayed, senior cleric Ahmad Alamolhoda confirmed that a selection has been made and will be revealed by the body’s secretariat.

Trump has previously dismissed the rumoured front-runner, Mojtaba Khamenei, as a "lightweight," insisting that the next leader must be someone who will "bring harmony and peace to Iran."

Iranian Foreign Minister Abbas Araghchi rejected the president's remarks on Sunday, stating that the leadership transition is "only the business of the Iranian people" and denouncing any foreign interference in the nation's internal affairs.

The regional war, now in its ninth day, has resulted in over 1,200 fatalities in Iran and six U.S. military deaths, as global energy markets continue to struggle with the blockade of the Strait of Hormuz.

With inputs from AFP