Toomaj Salehi, 33, was arrested in October 2022 for publicly backing the protests triggered by the death of Amini, a 22-year-old arrested by Iran's morality police for an alleged breach of strict dress rules for women.

The experts, who are independent of the UN, said they were "alarmed by the death sentence and the alleged ill-treatment of Mr. Salehi".

"Art must be allowed to criticise, to provoke, to push the boundaries in any society," they said in a statement.

The popular star was condemned to death by the Isfahan Revolutionary Court "on the charge of corruption on Earth", Iranian media reported Wednesday, quoting his lawyer.

"As harsh Mr. Salehi's songs are of the government," the experts said, he was only exercising his "artistic freedom and cultural rights".

They said Salehi was initially sentenced to six years in prison for his alleged role in the 2022 protests sparked by Amini's death, but was later released by Iran's Supreme Court.

However, he was held again in November last year for criticising the government and saying he was tortured while in custody.

Having been charged with "propaganda against the state", the experts said, Salehi has now been condemned to death.

The months of unrest following Amini's death on September 16, 2022, saw hundreds of people killed including dozens of security personnel, and thousands more arrested.

Iranian officials deemed the protests "riots" and accused Tehran's foreign foes of fomenting the unrest.

Nine men have been executed in protest-related cases involving killings and other violence against security forces.

After Amini's death, a growing number of women began appearing in public across the country without adhering to the dress code, with the morality police keeping a low profile.

But since April 13 Iran's police have started to toughen controls on women who flout the rules, according to local media.

The UN experts said it was becoming increasingly common in Iran for "artists, activists and journalists" to be arrested and charged with "publishing false news... or 'propaganda against the state'".

The independent experts -- five Special Rapporteurs and the five members of the Working Group on Arbitrary Detention -- are appointed by the Human Rights Council, though they do not speak on behalf of the UN.