Iranian police have arrested at least 12 people in connection with fresh protests in Khuzestan province.
Iranian media said the unrest was sparked when people took to the streets after being tricked by local conmen.
Five people were killed in riots last April over reports that Tehran wanted to change the ethnic balance of the area, home to about 2m ethnic Arabs.
The authorities are sensitive to reports of unrest in Khuzestan, which contains most of Iran's oilfields.
Reports in the Iranian press quoting local officials said rioting was provoked by thieves who took advance payments and then failed to deliver any goods.
However, a UK-based Arab separatist leader is quoted by Reuters saying that protests are building up to mark the 100th day after the April protests.
Mahmoud Ahmad al-Ahwazi, from the Ahvaz Arab People's Democratic-Popular Front, told Reuters that four people had been shot dead by police, but it is not possible to verify the claim.
Ethnic Arabs are thought to represent about 3% of Iran's population, but make up a majority in Khuzestan.
In a separate development, three Iranian police have died in an ambush by Kurdish insurgents near the northern border with Turkey, officials said.
Officials blamed the Turkish Kurdish rebels of the Kurdistan Workers' Party (PKK) for the violence, but did not give further details.