Tom Barrack, the US ambassador to Turkey, sparked controversy on Tuesday when he said Iran's government was "not an evil regime", an assessment that goes against years of messages from the administration of President Donald Trump.
The remarks by Mr Barrack, who is also Mr Trump's special envoy for Syria and Iraq, come as talks between the US and Iran remain stalled despite signs of increased diplomatic activity in Tehran.
At the Global Security Forum in Doha, Mr Barrack differentiated between Iran's ruling religious class and the actions of the Islamic Revolutionary Guard Corps, which he said “has become an adversary” and whose role with Israel “has been a problem”.
“It’s a theocracy," he said of Tehran's government. "It’s not an evil regime, that has nothing to do with it. That’s a religious content and practice that we all respect.”
The Trump administration has repeatedly used the word “evil” to describe Iran's regime, including in official White House statements and remarks by senior officials such as Defence Secretary Pete Hegseth.
The State Department did not comment. Secretary of State Marco Rubio told Breitbart News in a report broadcast on Sunday that Iran is "the number one driver of instability and war and conflict, and the number one obstacle to peace in the Middle East is the Islamic regime in Tehran".
On a visit to India on Tuesday, Mr Rubio compared Iran's tactics against commercial shipping in the Strait of Hormuz to those used by Nazi Germany's submarines during the Second World War.
Mr Barrack has a long record of provocative comments about governance in the Middle East and on other issues, including calling Hezbollah and Israel "equally untrustworthy", suggesting Israel "still" occupies the Golan Heights, and saying that Lebanon was at risk of becoming Bilad Al Sham again, the historical name for the Syria region.
Washington and Tehran remain locked in a conflict that started nearly eight months ago, with negotiations over reopening the Strait of Hormuz and Iran's nuclear programme at an apparent impasse.
Mr Barrack said the US should pursue a negotiated settlement rather than seek to impose regime change, saying Washington's previous attempts to change governments in the region had repeatedly failed.
“We’ve had 23 regime changes and none of them have worked,” he said. “Every time we try and intervene and change the person or the regime, it seems to have been a mistake.”
The remarks prompted a swift backlash from US conservative commentators, who accused Mr Barrack of playing down the Iranian government's repression and hostility towards Israel.
"Tom Barrack has gone rogue again, pushing his own insane agenda and giving aid and comfort to genocidal maniacs," said Mark Levin, a conservative broadcaster. "This has to be one of the most outrageous statements yet, about the mass killing, nuclear-obsessed Islamist terrorist Iranian regime."
Russia's Foreign Minister Sergey Lavrov met Iranian Foreign Minister Abbas Araghchi in Tehran on Monday, a day after the Russian minister held talks in Bahrain, where Gulf countries urged him to lobby Tehran to stop its drone and missile attacks on its neighbours.
In Iran, Mr Lavrov, who also met President Masoud Pezeshkian, said Russia was prepared to "assist in finding acceptable negotiated solutions" to resolve the crisis.
During Mr Rubio's visit to India, he also raised the prospect of Reliance Industries refining more Venezuelan crude and possibly increasing its involvement in oil production in the country.
The US is looking to boost global oil supplies to ease shortages caused by the war with Iran and Russia's war against Ukraine.
