PESHAWAR (AP): Troops foiled a suicide attack on a vital road tunnel in northwestern Pakistan on Friday, firing on a speeding vehicle that exploded and injured 20 people, police said.

Paramilitary troops guarding the Kohat Tunnel shot at the car after its driver ignored signals to stop, said Afzal Khan, a local police official.

Flying debris from the subsequent blast wounded 20 people, most of them troops but also several civilians, Khan said. Only the bomber was killed.

Violence has surged in Pakistan's border region as the country's leaders jockey for power in the wake of Pervez Musharraf's resignation as president.

More than 200 people have died in Taliban bombings and clashes since the longtime U.S. ally quit Aug. 18 and triggered a power struggle that caused the country's ruling coalition to collapse.

The Kohat Tunnel links the regional capital of Peshawar with garrison towns on the edge of Pakistan's lawless tribal regions, from where Taliban and al-Qaida militants attack targets in Afghanistan and Pakistan.

Troops are posted at both ends of the tunnel and check every vehicle seeking to pass through out of concern militants could use a bomb to block it.

Mohammed Siraj Khan, a government official in Kohat, said security forces arrested a local Taliban commander named Mohammed Ajmal and three of his associates at the tunnel on Thursday.

``It seems the militants are angered over these arrests, and they wanted to avenge it by targeting security forces,'' he said.