"A group of 40 terrorists who had infiltrated the Haj Omran area near Piranshahr were caught in our fire, resulting in 12 of them killed and a number injured and the rest escaped," Fars quoted a West Azerbaijan police information officer, Shahnam Rezaei, as saying.

He said four Iranian border patrol police also died in the shoot-out and one was wounded, but gave no further details or the date of the clash.

Jomhouri Islami newspaper reported on Monday, that four members of the Iranian security forces were killed by mines laid by Kurdish separatist rebels in the northwest of the country.

The newspaper said the radio-detonated mines had been planted in the Haj Omran region close to the border with Iraq by rebels from the Party of Free Life of Kurdistan (PJAK).

There has been an apparent increase in fighting with the Kurdish rebels on Iran's northwestern borders with Iraq and Turkey over the past few weeks.

Iranian security forces on Friday killed three PJAK members in clashes in the northwest of the country, news agencies reported.

Last week, it was reported that six members of Iran's elite Revolutionary Guards died in fighting with PJAK while two border guards were killed by mines laid by the rebels.

The group operates from rear-bases in northeastern Iraq and makes sorties across the border into Iran. It has been involved in a series of clashes with Iranian security forces in recent years.

The rebel group has close links to the Kurdistan Workers' Party (PKK), which has waged a deadly insurgency in southeastern Turkey since 1984.