Different security and intelligence forces detained the protesters, making it difficult to know the exact number of detainees, Sadeghi was quoted as saying.
About 1,000 were previously reported to have been arrested during almost a week of demonstrations that began in December.
Violence broke out at several rallies, leaving at least 22 people dead.
The unrest spread to more than 80 cities and rural towns late last month as thousands of young and working class Iranians voiced anger at corruption, unemployment, and a deepening gap between rich and poor in the biggest anti-government demonstrations since 2009.
Grievances also seemed to revolve around Iran's foreign policy and its spending on groups in Syria, Lebanon and Gaza.
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What's driving the protests in Iran?
The protests started in the Iran's second-largest city of Mashhad on December 28 before spreading to other cities.
The provincial governor in northeastern Mashhad was quoted as saying that 85 percent of detainees there had been released after signing a pledge not to re-offend.
Iranian authorities have accused the United States, Israel and Saudi Arabia of involvement and orchestrating the anti-government demonstrations.
The government restricted access to Instagram and Telegram social media apps as a security measure.
On January 3, General Mohammad Ali Jafari, head of Iran's Islamic Revolutionary Guards Corps (IRGC), declared "the end of the sedition".
Tens of thousands also took part in pro-government rallies to show support for the Iranian leadership.
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