An Iranian official said Friday that 52 people had been arrested at protests the previous day in Mashhad as the government suggested hardline opponents may have been behind the unrest.
Reformist media said hundreds had taken to the streets of Mashhad and other towns on Thursday in protest at high prices and unemployment, directing their anger against President Hassan Rouhani's government.
The head of Mashhad's revolutionary court, Hossein Heidari, said people were arrested for chanting "harsh slogans", the Fars news agency reported.
First Vice-President Eshaq Jahangiri said Friday that "some incidents in the country these days are on the pretext of economic problems, but it seems there is something else behind them".
In comments carried by state broadcaster IRIB, he said those responsible must be identified, adding that efforts to stir unrest would "backfire".
"They think by doing this they harm the government," he said, but "it will be others who ride the wave".
Conservative opponents of the government have focused on the struggling economy, trying to paint Rouhani's liberalizing efforts as only benefiting the rich.
Rouhani, who won a second term in May, has sought to clean up Iran's chaotic banking sector, rebuild foreign trade and bring inflation under control -- but for many the results have been too slow to materialize.
Videos of the protests in Mashhad, a pilgrimage destination in Iran's northeast, showed people chanting "Death to Rouhani".
The footage, published by small reformist media group Nazar, also showed people shouting "not Gaza, not Lebanon, my life for Iran", reflecting anger in some circles that the government is focusing too much on regional politics rather than tackling domestic problems.
Protests took place in several other cities in response to calls on the Telegram messaging app for demonstrations against high prices.
But one lawmaker in the region said there were other reasons behind the protests.
"There is a major crisis in Mashhad caused by illegal financial institutions," Hamid Garmabi, who represents the city of Neyshabour near Mashhad, told Fars.
Unauthorized lending institutions mushroomed under former president Mahmoud Ahmadinejad due to weak regulation of the banking sector.
An uncontrolled construction boom left many credit companies stuck with toxic debts and unable to repay investors.
Since coming to power in 2013, Rouhani has shut down three of the biggest new credit institutions -- Mizan, Fereshtegan and Samen al-Hojaj.
He tasked the central bank with reimbursing lost deposits, but many are still waiting for compensation.
Mashhad was among the areas hardest hit by the closure of Mizan, which had around one million accounts, according to the official IRNA news agency.