BEIRUT (Reuters) - Eight Iranian border guards were killed by militants in a cross-border raid on the frontier with Pakistan on Monday, according to reports in the Iranian media.

Sistan-Baluchestan province in southeast Iran has long been plagued by unrest from both drug smuggling gangs and separatist militants. The population of the province is predominantly Sunni Muslim while the majority of Iranians are Shiites.

"The armed terrorists entered Iranian soil from Pakistani soil and clashed with the guards," Ali Asghar Mirshekari, the deputy governor of the province, told the IRNA news agency.

"They killed eight members of the border guards and fled to Pakistani soil."

The attack happened only two days before Foreign Minister Mohammad Javad Zarif was scheduled to visit Pakistan.

Tasnim Aslam, a spokeswoman for the Pakistani Ministry of Foreign Affairs, condemned the attack and said a militant group called Jaish al Adl had claimed responsibility, according to Iranian state media.

"It’s necessary that the two countries work together on this issue in order to maintain security in the border areas," she said.

Local journalists in Baluchistan's Chagai district said a man claiming to be from Jaish al Adl had sent them a message claiming responsibility for the attack.

Jaish al Adl is a Sunni militant group that has carried out attacks against Iranian security forces with the aim of highlighting what they say is discrimination against Sunni Muslims and the ethnic Baluch in the province.

It claimed responsibility for an attack that killed 14 border guards in October 2013.