Videos posted on social media showed scores of protesters marching in Tehran and other Iranian cities in what was said to be the biggest show of force by opponents of the clerical establishment in years.
Rallies in Tehran and Iran’s second city, Mashhad, can be seen in footage verified by BBC Persian, with peaceful demonstrations not dispersed by security forces.
On Wednesday, there were violent clashes in several cities.
Crowds in Mashhad called for the overthrow of the Supreme Leader, Ayatollah Ali Khamenei, and the return of Reza Pahlavi, the exiled son of the former shah, urging his supporters to take to the streets.
It was the 12th consecutive day of unrest in Iran that saw protests spread to 140 cities and towns in all 31 provinces, according to the US-based Human Rights Activist News Agency (HRANA).
It was reported that at least 34 protesters and seven security personnel were killed during the unrest, and that 2,270 protesters were arrested.
Another group, the Norway-based Iran Human Rights said at least 45 protesters, including eight children, were killed by security forces.
BBC Persian confirmed the deaths and identities of 21 people, while Iranian authorities reported the deaths of five security personnel.
The protests began on December 28, when shopkeepers took to the streets of the capital, Tehran, to express their anger at another sharp fall in the value of the Iranian currency, the rial, against the US dollar on the open market.
The rial fell to a record low last year and inflation soared to 40% as sanctions over Iran’s nuclear program squeezed an economy also weakened by government mismanagement and corruption.
University students soon joined the protests and they began to spread to other towns, with crowds often heard chanting slogans against the clerical establishment.