Rebels killed three members of the Iranian security forces in a violence-plagued southeastern region near the border with Pakistan, state news agency IRNA reported.
The attack happened on Wednesday afternoon in the border province of Sistan-Baluchistan.
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"Armed rebels called the police emergency line and when members of the security forces went there they were killed in cold blood," General Hossein Rahimi, head of the provincial security forces, was quoted as saying.
Sistan-Baluchistan, which has a large Sunni Muslim community in an otherwise predominantly Shiite country, often sees violence involving Sunni extremists and drug smugglers.
Last month an Iranian soldier was killed and two pro-government militiamen were wounded in an attack blamed on the Sunni extremist group Jaish-ul Adl (Army of Justice).
The same group captured five Iranian soldiers in February, four of whom were released in April. The fate of the other man remains unknown.