Four members of Iran’s Islamic Revolutionary Guard Corps were killed on Monday in what state media has called a terrorist attack.
“Terrorist groups” attacked IRGC members in the border area of Saravan before being forced into Pakistan, the Irna news agency said, citing corps officials in the south-east.
No details were given on the groups involved.
Saravan is in Sistan and Baluchestan province, which has seen some of the worst bloodshed since anti-government protests erupted three months ago.
Additional IRGC units have been deployed to the Kurdish west and Baloch south-east, where Tehran has accused “terrorist groups” of fomenting the popular unrest.
Sistan and Baluchestan is mainly populated by the Baloch minority, present in both Iran and across the border in Afghanistan and Pakistan.
In October, the Taftan border crossing was sealed off as Iranian security forces gunned down almost 100 people in the provincial capital, in what has become known as Zahedan's “Bloody Friday”.
The border crossing is a vital trade route and is also used by pilgrims heading to Iran.
The IRGC has been the backbone of Tehran's crackdown on protesters, who took to the streets following the death of Mahsa Amini in morality police custody in September.
Nearly 500 have been killed since the protests began, according to rights groups. The UN estimates at least 14,000 have been arrested, several of whom have already been executed for joining the protests.