DERA ISMAIL KHAN, Pakistan - A suicide bomber has killed at least 18 people in northwestern Pakistan.

Officials say the bomber blew himself up while travelling in the back of a pickup truck crowed with passengers.

They say the bomber boarded the truck as it travelled to a village near the city of Dera Ismail Khan.

Police stopped the truck and challenged the man because they thought he was acting suspiciously.

But when they told him to climb down from the truck, he detonated his explosives.

City Councillor Malik Khan Zaman says two policemen are among the dead.

Interior Ministry spokesman Brig. Javed Iqbal Cheema said 16 people were killed and 16 wounded. Dr. Ahsan Waheed at a local hospital where the victims were taken said 18 were killed and another 18 wounded, four seriously.

Television footage showed blood splattered at the scene and damage to several nearby vehicles, including a jeep. Police were seen collecting body parts in plastic bags.

According to witnesses, the bomber appeared to be no more than 15 years old, a police official said on condition of anonymity.

The bombing is the latest in a spate of militant attacks in Pakistan's borderlands near Afghanistan where pro-Taliban fighters have gained sway and pose a growing threat to the authority of the state.