Hollywood actors including Mark Ruffalo have taken up the case of Peyvand Naimi, 30, who they say is charged with offences he could not have committed.

The Bahais are Iran's largest non-Muslim religious minority but have never been recognised under the constitution of the Islamic republic, and say they have been persecuted since it was created in 1979.

The Bahai International Community (BIC) group, which represents Bahai interests at the UN, said that Naimi was arrested in January in the southeastern city of Kerman on false charges of instigating unrest.

"He faces imminent danger after enduring two mock hangings, prolonged torture and interrogation, as Iranian authorities attempt to force him to confess to crimes he did not commit," it said.

He was forced to confess in footage broadcast on Iranian television and then faced a "preposterous" accusation of involvement in killing security forces in Kerman, even though these incidents took place while under arrest, it said.

While in prison he was also accused of celebrating the killing of supreme leader Ali Khamenei in an airstrike on February 28 at the start of the US-Israeli war against Iran, although he had no way of finding out the news behind bars, the BIC added.

Iran earlier this month executed three men accused of killing police officers during the protests in January.

"Peyvand has been falsely accused of multiple crimes as part of a systematic effort by an unjust government to blame Bahais for the unrest during the January protests in Iran," Ruffalo said in a video with fellow actors Penn Badgley and Rainn Wilson posted to his Instagram account this week.

Badgley and Wilson are both converts to the Bahai faith, while Ruffalo's father was a Bahai. While not a Bahai himself, the actor is a supporter of Bahai rights and human rights.

Describing the mock executions, he said: "The first one they put a rope around his neck and told him to say his last prayers and then stopped."

"The second mock hanging escalated to the point that the stool was almost kicked out from beneath his feet."

"Bahais like Peyvand are peace builders. Peyvand has committed no crime, stirred up no unrest and has harmed no one," said Ruffalo, calling for an "end to the senseless scapegoating" of the Bahai in Iran.

How many members of the community remain in Iran is unknown, but activists believe there could still be several hundred thousand.

The Bahai faith is a relatively young monotheistic religion with roots dating back to the early 19th century in Iran.

Members have repeatedly faced charges of being agents of Iran's arch-foe Israel, which activists say are baseless.