Ethnic unrest has broken out in Iran's south-western province of Khuzestan, according to Iranian media.
One newspaper reported that around 200 protesters gathered in the city of Ahvaz to shout anti-government slogans.
Iranian news agency Mehr said protesters in traditional Arabic dress threw bottles and rocks at police before ringleaders were arrested.
Iran blamed bomb blasts last month and in June across the region, which borders on Iraq, on UK agents.
In April, days of rioting by ethnic Arabs in the oil-rich province led to several deaths and hundreds of arrests after protests at government plans to encourage more ethnic Persian Iranians to move to the province.
The province is home to about two million Arabs.
Iran said the violence in the province was foreign-instigated, adding that several people with links to the UK had been arrested.
The unrest in April revealed a glimpse of deep ethnic tensions, says the BBC's Frances Harrison in Tehran.
She says the subject was so sensitive that the office of the Arabic language television station Al Jazeera was closed and has not yet been allowed to reopen.
The authorities are sensitive to reports of unrest in Khuzestan, which contains most of Iran's oilfields.