The protests were the most violent since June's disputed elections
Iran has said several foreign nationals were arrested during anti-government demonstrations last week.
Intelligence Minister Heydar Moslehi said those detained had been "pursuing propaganda and psychological warfare". He did not give their nationalities.
Some 300 of the 500 people arrested remain in detention after mass protests in Tehran on 27 December during the Shia Muslim festival of Ashura.
At least eight people were killed in a crackdown on anti-government protests.
"Several foreigners are among those arrested on the day of Ashura, they were leading a psychological war against the system," Mr Moslehi told state television.
"They entered Iran two days before Ashura," he added.
The late December demonstrations were the country's most violent protests since those following June's disputed presidential election. The nephew of opposition leader Mir Hossein Mousavi was among those killed in the clashes.
No further details about those arrested were available.
According to a pro-government website, Rajanews, a "British citizen, who was carrying his passport" was among those arrested, AFP reports.
The news agency also says an Iran-based Syrian journalist working for Dubai TV was also among those detained.
Press TV also had reported that those arrested also included members of the banned militant opposition group Mujahideen Khalq Organisation (MKO) - or the People's Mujahideen.
The protests, which began after President Mahmoud Ahmadinejad's controversial re-election in June, have grown into the biggest challenge to the government since the 1979 Islamic revolution.