Iran's elite Revolutionary Guards killed 12 Kurdish rebels near the Iraqi border in clashes in which three Guards were also killed, an Iranian news agency reported on Thursday.
Wednesday evening's fighting took place in Oshnavieh in the northwest, the Tasnim news agency said, citing a statement from the Guards.
Two separate groups of rebels had slipped across the border to carry out acts of "sabotage" and "create insecurity among the population", it added.
Oshnavieh lies around 20 kilometres (12 miles) from the border with the autonomous Kurdish region of northern Iraq.
Iran's top police officer, General Hossein Ashtari, said the fighters killed were members of PJAK -- the Party of Free Life of Kurdistan, an Iranian Kurdish group with close links to Turkey's outlawed Kurdistan Workers' Party (PKK).
"A large quantity of arms and ammunition was seized from this terrorist group," Ashtari told Tasnim.
The incursion comes days after five Kurdish rebels and five jihadists were killed, along with a police officer, in separate clashes in the northwest and southeast of Iran.
"A team of five from the PJAK terrorist splinter group... has been identified and destroyed in the Sardasht region" on the Iraqi border, a Guards statement said on Monday.
Later that day, state television reported six more deaths in armed clashes in Sistan-Baluchistan province in the southeast.
One police officer and five militants were killed in the fighting, which pitted Iranian forces against Sunni militant group Jaish-ul Adl.