US President Donald Trump says Iran has “made a big mistake” by choosing Mojtaba Khamenei as the country’s new supreme leader after his father, Ali Khamenei, was killed in a US-Israeli strike at the start of the war, according to an interview with NBC News.

In a phone interview on Monday, Trump criticised Tehran’s decision to elevate the 56-year-old cleric, who is widely seen as a hardliner.

“I think they made a big mistake,” Trump said of the decision. “I don’t know if it’s going to last. I think they made a mistake.”

Trump also left open the possibility that the United States could seek control of Iranian oil resources, though he said it was premature to discuss such a move.

He told NBC News he did not want to elaborate on whether Washington might seize Iranian oil but acknowledged the idea had been discussed.

“Certainly people have talked about it,” Trump said.

He pointed to recent US actions in Venezuela, where the United States carried out a raid earlier this year that captured the country’s leader, Nicolás Maduro. Trump said the US had since taken steps to access Venezuelan oil reserves.

“You look at Venezuela,” he said. “People have thought about it, but it’s too soon to talk about that.”

The remarks come as global energy markets react to the ongoing conflict involving the United States, Israel and Iran. Oil prices surged above $100 per barrel over the weekend following the escalation.

Iran is the world’s ninth-largest oil producer, accounting for roughly five per cent of global output, while about 80 per cent of its crude exports go to China.

During the interview, Trump also discussed domestic political issues, including the proposed SAVE America Act, a bill that would tighten voting requirements by mandating proof of citizenship for voter registration across the United States.

The legislation has already passed the House of Representatives but faces significant hurdles in the Senate, where it would require 60 votes to overcome the filibuster rule.

“I’m focused on one thing, and that’s the vote” on the SAVE America Act, Trump said.

Asked whether Congress would ultimately pass the measure, he replied: “I don’t know.”

“Nobody is doing much on it,” he added. “And until they do, I’m not doing anything.”

Trump also attended a “dignified transfer” ceremony over the weekend at Dover Air Force Base in Delaware, where the remains of six US service members killed in the Iran war were returned from the Middle East.

Wearing a “USA” cap, the president saluted as the flag-draped containers arrived and later met privately with the families of the fallen troops.

“They are great people,” Trump said.

“It’s always tough.”