The official IRNA news agency said 10 other security force members were injured.
It said the fighting erupted overnight in Sistan and Baluchistan province when gunmen opened fire on a Revolutionary Guard post in Rask town and a coast guard station in Chahbahar city, some 1,400 kilometers (870 miles) southeast of the capital, Tehran.
IRNA said six assailants were under siege and holding hostages at the two sites. It did not elaborate on the hostages, but it blamed the attacks on the militant group Jaish al-Adl, which allegedly seeks greater rights for the ethnic Baluch minority.
The restive area, bordering Afghanistan and Pakistan, has been the site of occasional deadly clashes involving the militant group, armed drug smugglers and Iranian security forces. In December, militants killed nearly a dozen police officers in an attack on a police station in the province.
The area is one of the least developed parts of Iran. Relations between the predominantly Sunni Muslim residents of the region and Iran's Shiite theocracy have long been strained.
Militants killed at least 5 Iranian security officers and wounded another 10 in two separate attacks on military installations in southeastern Iran, state media reported on Thursday.
The attacks by militants from the Jaish Al-Adl group took place overnight and targeted Iranian Revolutionary Guards headquarters in Rask and Chabahar, located in the Sistan and Baluchistan province, the reports said.
At least eight militants were killed during exchanges of fire with security forces, the media reports said.
Jaish Al-Adl is an extremist militant group that operates in southeastern Iran and the western Pakistani province of Balochistan.
In January, Iran targeted two bases of the militant group in Pakistan with missiles, prompting a rapid military riposte from Islamabad targeting what it said were separatist militants in Iran.