As Iranian riot police lined up to confront anti-regime demonstrators, a young woman wearing jeans and a pink headscarf defiantly marched up to the officers and screamed: “Death to Khamenei.”

A crowd nearby followed suit, shouting slogans against Ayatollah Ali Khamenei. Video footage of the incident in the historic city of Isfahan on Friday went viral, and similar chants against the Islamic republic’s supreme leader have become a feature of the five days of unrest.

The diatribes launched against Mr Khamenei underline the unusual nature of the protests that have become the biggest challenge to the regime in almost a decade. Public criticism of the supreme leader has been a taboo subject since the Islamic revolution, and was barely raised by protesters during the last big anti-government demonstrations in 2009.