Militants attacked a gas field in troubled south-west Pakistan and 12 of them were killed in fighting with security forces, a senior government official says. Three soldiers were killed and three wounded in an earlier landmine blast in the region where separatist tribal fighters have been battling for control of resources for decades. "Up to 40 militants attacked a gas field. During the fighting 12 militants were killed," Abdul Samad Lasi said, the top administration official in the area. Baluch militants have been waging a low-level insurgency for decades for greater benefits and control of gas and other natural resources. The gas field, near the small town of Pir Koh, was not damaged, Mr Lasi says. The landmine was planted on a road in the same area and exploded when the troops' vehicle ran over it, he says. Two soldiers were killed instantly and one died later.