Trump calls Iran's appointment of Mojtaba Khamenei as new supreme leader 'a big mistake'

US President Donald Trump expressed displeasure Monday over Iran's appointment of Mojtaba Khamenei as its new supreme leader, calling it "a big mistake."

"I don't know if it's going to last ... I think they made a mistake," Trump told NBC News. He had earlier told the New York Post he was "not happy" with the choice.

"He's going to have to get approval from us," Trump also said.

Mojtaba Khamenei, 56, on Sunday became Iran's third supreme leader since the 1979 revolution, succeeding his father Ayatollah Ali Khamenei, who was killed in a US/Israeli airstrike on his Tehran compound on Feb. 28 after holding the position for 37 years.

Trump also declined to rule out seizing Iranian oil but said it was premature to discuss the matter.

"Certainly people have talked about it," he said, pointing to Venezuela as a precedent, where the US secured more than 80 million barrels of oil after capturing Venezuelan leader Nicolas Maduro earlier this year.

"It's too soon to talk about that," he added, on Iran.