Ten Iranian border guards were killed by Sunni militants in a cross-border attack on the frontier with Pakistan on Wednesday, Tasnim news agency reported.
The militant group called Jaish al Adl, or the Army of Justice, has claimed responsibility, the report said.
"Ten border guards of Mirjaveh county in Sistan and Baluchestan Province were martyred in an ambush by the terrorists in the Pakistani border's zero-point," Tasnim said.
In a statement carried on state media, the Iranian police said the guards were killed by long-range guns and "the Pakistani government bears the ultimate responsibility of the attack."
Sistan-Baluchestan province in southeastern Iran has long been plagued by unrest from both drug smuggling gangs and separatist militants. The population of the province is predominantly Sunni Muslim; the majority of Iranians are Shiites.
Jaish al Adl is a Sunni militant group that has carried out several attacks before against Iranian security forces with the aim of highlighting what they say is discrimination against Sunni Muslims and the ethnic Baluch in the province.
The group claimed responsibility for attacks that killed eight border guards in April 2015 and 14 border guards in October 2013.
With your current subscription plan you can comment on stories. However, before writing your first comment, please create a display name in the Profile section of your subscriber account page.