Three suicide bombers in explosive-laden vehicles were spotted by the security forces near the Japanese-built Kohat tunnel and ordered to stop. When they did not heed, the security forces opened fire, TV channels reported.

One vehicle blew up when it was hit by the security forces, while another exploded after hitting a wall. The occupants of both vehicles were killed.

The third would-be bomber abandoned his vehicle and fled from the area, reports said.

About 20 security personnel, who were injured in the fire fight were shfted to the local military hospital for treatment.

Kohat tunnel, links North West Frontier Provinces capital Peshawar to southern parts of the province, has been sealed. Taliban militants have made several attempts to attack the tunnel over the past few months in a bid to disrupt vital transport and communication links in the NWFP.