President Donald Trump in an announcement Monday said the US was imposing sanctions on Iran's Ayatollah Khomeini — who has been dead since 1989.

The sanctions in fact apply to Iran's current supreme leader, Ayatollah Ali Khamenei. The mix-up was seized upon by his critics.

After the sanctions against Khamenei were announced, Iranian President Hassan Rouhani said the Trump White House had "mental retardation."

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President Donald Trump on Monday mistakenly named a supreme leader of Iran who has been dead since 1989 as the target of new US sanctions.

By mispronouncing one syllable in a press conference in the Oval Office, Trump said he was sanctioning "Ayatollah Khomeini" of Iran.

He meant to name Ayatollah Ali Khamenei, the current supreme leader, as confirmed by a White House transcript and an announcement by the US Treasury.

Khomeini ruled Iran as supreme leader from the Islamic Revolution in 1979 until his death in 1989.

Iran's Ayatollah Khomeini seen in 1984 in Iran. He took power after the Islamic Revolution and died in 1989. Francois LOCHON/Gamma-Rapho via Getty Images

In a video, Trump said (emphasis ours):

"Sanctions imposed through the executive order that I'm about to sign will deny the supreme leader and the supreme leader's office, and those closely affiliated with him and the office, access to key financial resources and support. The assets of Ayatollah Khomeini and his office will not be spared from the sanctions."

—The White House (@WhiteHouse) June 24, 2019

The one-syllable difference is somewhat less apparent when comparing the men's full names: Sayyid Ruhollah Musavi Khomeini was the first ayatollah, and Sayyid Ali Hosseini Khamenei is the second.

On Twitter, critics were quick to question the discrepancy.

—Murtaza Mohammad Hussain (@MazMHussain) June 24, 2019

The sanctions imposed Monday came amid escalating tensions between Iran and the US, with Trump ordering and then calling off airstrikes last week against Iran after it downed a US drone.

Targeting Iran's head of state clearly touched a nerve.

In a Tuesday speech broadcast live on Iranian TV, Hassan Rouhani, the president of Iran, said the Trump White House had "mental retardation."