"Preliminary investigations show that this terrorist act was brutally carried out by anti-revolutionary forces," Kheyrollah Moradi, head of the provincial environmental organisation, was quoted as saying.

He said the four went missing from an area called Dooshan at about 09:30 am (0600 GMT) on Friday, and their bodies were found after seven hours.

Western Iran, home to a significant Kurdish population, has been the scene of deadly clashes for years between security forces and Kurdish rebel groups operating from bases in neighbouring Iraq.

In September 2010, a deadly bombing hit a military parade in the western city of Mahabad in Kurdistan, killing 12 people and wounding at least 81.