Eighteen people, including two policemen and a soldier, were killed and several others injured on Tuesday when a suicide bomber blew himself up in a minibus as police tried to search him for explosives in a north-west Pakistani town.

The incident occurred in Dera Ismail Khan in North West Frontier Province when security personnel tried to search the bomber who was acting suspiciously, area Superintendent of Police Khaled Mohammed told TV channels.

He said the bomber had alighted from a bus, which came to the town from Tank -- a city in the troubled South Waziristan tribal agency near Afghan border, and ran towards another passenger coach to escape the approaching security personnel who wanted to search him.

Police also entered the minibus following which the bomber exploded, causing casualties among security personnel and passengers, he said.

Area Police Chief Haji Habib-ur-Rehman said two policemen and a paramilitary soldier were among the 18 people killed in the blast while 15 others injured.

He said the bomber, a teenager, wanted to carry out a suicide attack somewhere else.

The Dera Ismail Khan town has witnessed a spate of suicide attacks and bomb blasts in recent months.

About 30 people, most of them polic men, were killed and 56 others injured when a suicide bomber detonated explosives strapped to his body at a police recruitment centre in the town in July.

Bomb blasts and suicide attacks have increased in Pakistan's northwest and tribal regions after the local militants scrapped a peace deal with the government in July.

The militants are also angry at the July 11 army operation against Islamabad's Red Mosque in which over 100 people were killed.