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An attack, which was later claimed by a militant group, killed a policeman in restive southeastern Iran on Wednesday, state media reported.

Sistan-Baluchistan province, where the attack took place, has seen persistent unrest involving drug-smuggling gangs and rebels from the Baluchi ethnic minority as well as jihadists.

"In an exchange of fire this morning between forces from a police station in Rask and members of an armed group, one of the policemen was killed," Iran's official IRNA news agency reported.

The news agency said the firefight lasted around three hours before the arrival of police reinforcements prompted the assailants to withdraw.

The attack was claimed by militant group Jaish al-Adl (Army of Justice) in a brief statement on its Telegram channel. Jaish al-Adl was formed in 2012 and is blacklisted by Iran as a "terrorist" group.

It was the second deadly attack on security forces in Rask claimed by the group in recent weeks.

At least 11 officers were killed in a similar attack on a police station in the town before dawn on December 15.

Sistan-Baluchistan province borders Pakistan and Afghanistan and has long been regarded as a key access point for militant groups, drug smugglers and irregular migrants.

Last week, Interior Minister Ahmad Vahidi announced new measures to firm up security along the porous border, following twin suicide bombings claimed by the Islamic State group that killed more than 90 people at a high-profile state event in the southern city of Kerman.

Vahidi said authorities had identified "priority points to block along the border".