Militants killed 10 Iranian Revolutionary Guards in an attack on a post on the Iraqi border on Saturday, Iran's semi-official Tasnim news agency reported, the latest deadly clash in an area where armed opposition Kurdish groups are active.
The agency quoted a Revolutionary Guards statement as saying that several of the attacking "terrorists" were also killed in the fighting in which a munitions depot was blown up.
Provincial security official Hosein Khosheqbal told state television that 11 members of the Guards' voluntary Basij forces were killed in the overnight violence in the Marivan area, which he blamed on the Kurdish armed opposition group PJAK.
"The latest news is that the Basij and Guards forces are in hot pursuit of the attackers," Khosheqbal said.
The Party of Free Life of Kurdistan (PJAK) -- an outlawed group that seeks self-governance for Iran's Kurds and has links to Turkey's militant Kurdish Workers' Party (PKK) -- operates in the border area, along with other armed Kurdish groups based in northern Iraq.
Earlier this month, the Revolutionary Guards said they had killed three militants in a security operation near the border with Iraq, and nine militants were reported killed by the Guards last month further north on the border.
There is little coordination between Iranian and Iraqi forces over security of the porous border that has also been used by Islamic State to enter Iran.
Intelligence Minister Mahmoud Alavi said on Tuesday that security forces in southwest Iran arrested four suspected Islamic State operatives who were planning attacks.
In June 2017, Islamic State militants carried out coordinated attacks at the parliament building in Tehran and the mausoleum of Iranian revolutionary leader Ayatollah Ruhollah Khomeini south of the capital, killing at least 18 people.