Four people have been killed when a pick-up truck laden with explosives blew up outside a police station in north-western Pakistan.

The blast destroyed several shops and homes and damaged the station and a nearby mosque in the town of Badh Ber, which lies close to a Pakistani air force base as well as the major north-western city of Peshawar. Thirty other people were injured.

The area has become the focal point for militant retaliation against an army offensive along the nearby Afghan border.

Militants have killed more than 300 civilians and security personnel in the last month to try to weaken the country's resolve to continue its military operation in South Waziristan, where al Qaida and Taliban leaders are believed to be hiding.

"We have to continue this war against terrorists and have to keep our nerves," said Mian Iftikhar Hussain, the information minister for North West Frontier Province, where Badh Ber is located.

Police opened fire on the pick-up truck as it approached a checkpoint in front of the police station, but the driver was able to detonate his explosives, said Peshawar police chief Liaqat Ali Khan.

"The sound of the blast was very loud, and when I rushed out from my home I saw everything was destroyed here," Tariq Hasan told AP Television News.

The attack killed four people and wounded 30 others, said Sahib Gul, a doctor at a hospital in Peshawar where the victims were taken. The identities of the dead were not known.

Local television footage showed rescue workers searching for survivors amid a tangle of bricks and twisted metal. The blast also killed a horse which was attached to a wooden carriage and injured another nearby.

Police explosives expert Tanvir Ahmed estimated the truck was carrying about 550lb (250kg) of high explosives, a much larger amount than has been used in other bombings carried out in recent weeks.