A Revolutionary Guard colonel is among 19 people killed during heavy gun battles in the southeastern Iranian province of Sistan-Baluchistan.
"Nineteen people were killed and 20 wounded in the incident," regional governor Hossein Khiabani told the state broadcaster late on Friday.
"Provincial intelligence officer of the Islamic Revolutionary Guard Corps Colonel Ali Mousavi was also killed," state television added.
Earlier on Friday, state media reported that security forces had returned fire when a police station in the provincial capital Zahedan came under attack by gunmen.
"A number of police members, as well as passers-by, have been injured in the exchange of fire," the state broadcaster said.
Poverty-stricken Sistan-Baluchistan, which borders Afghanistan and Pakistan, is a flashpoint for clashes with drug smuggling gangs, as well as rebels from the Balochi minority and militant groups.
European citizens arrested
It was not immediately clear whether the clashes were connected to the wave of unrest that has swept Iran since the death of Kurdish woman Mahsa Amini in police custody earlier this month.
Iran, which has blamed "foreign enemies" for women-led protests said on Friday it had arrested nine European nationals for their role in the unrest.
The detention of citizens of Germany, Poland, Italy, France, the Netherlands, Sweden and other countries is likely to ratchet up tensions between Iran and Western countries.
Tehran has responded to international condemnation of the case by lashing out at its critics, accusing the United States of exploiting the unrest to try to destabilise Iran.