A number of people were held for trying to damage public property, he said.
Fars reported that protesters in Kermanshah chanted anti-government slogans such as "never mind Palestine, think about us", "death or freedom" and "political prisoners should be freed".
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 's government. Many Iranians now say they agree with Supreme Leader Ayatollah Ali Khamenei's repeated warnings the USA can't be trusted.
Iran's state-run IRNA news agency quoted the governor of the northeastern city of Mashhad, Mohammad Rahim Norouzian, as saying there was an illegal "No to high prices" gathering in the city.
They were among a group of 50 people who gathered in a city square, Tehran's deputy governor-general for security affairs told the Iranian Labour News Agency. Protesters were filmed shouting anti-government slogans such as "death to the dictator" and "death to Rouhani".
The semi-official Fars news agency reported that officials said around 300 protesters gathered in the western city of Kermanshah, the scene of a devastating quake in November that killed over 600 residents.
In social media footage, which could not be authenticated, riot police were seen using water cannon and tear gas to disperse crowds. Iranians based out of Tehran, Khorasan Razavi, Khuzestan, Fars and Isfahan provinces tweeted more than 11,000 times since the protests began on December 27.
However, he noted that a call for "No to high prices" protests had been circulated on the messaging app Telegram.
Some protestors have also criticized Iran's support of Syrian President Bashar Assad in his country's civil war, in which the Iran's powerful Revolutionary Guard has played a major role.
Vice-President Eshaq Jahangiri, a close Rouhani ally, suggested that hardline conservative opponents of the pragmatist president might have triggered the protests but lost control of them.
Rouhani's leading achievement, a 2015 deal with world powers that curbed Iran's disputed nuclear program in return for a lifting of most worldwide sanctions, has yet to bring the broad economic benefits the government says are coming.
So has inflation, which Iran's Central Bank says has returned to 10 percent.
Out of a total Iranian population of 80 million, some 3.2 million are jobless, according to official data.