Four Iranian policemen were killed on Sunday after attackers fired on a patrol in the restive southeastern province of Sistan-Baluchistan near the border with Pakistan, state media reported.
"Three policemen were martyred in a terrorist attack on a police patrol unit," state news agency IRNA reported.
A fourth died later after succumbing to his wounds, state television reported.
The circumstances of the attack were not immediately clear.
Unrest in the impoverished Sistan-Baluchistan province has involved drugs-smuggling gangs, rebels from the Baluchi minority and Sunni Muslim extremist groups.
On July 8, two policemen and four assailants were killed in a grenade and gun battle in the province during an attack later claimed by the jihadist Jaish al-Adl group.
In May, five Iranian border guards died in clashes with an armed group in Saravan southeast of Zahedan, the provincial capital of Sistan-Baluchistan.
State media reported at the time that the attack was carried out by "a terrorist group that was seeking to infiltrate the country" but whose members "fled the scene after suffering injuries".
In late May, IRNA quoted a police official, Qassem Rezaee, as saying "Taliban forces" had shot at an Iranian police station in Sistan-Baluchistan, a drought-parched region which also borders Afghanistan. The two countries have been arguing over water rights.
Zahedan was also the scene of protests that flared last September, with dozens of deaths, over the alleged rape of a teenage girl by a police officer.