PESHAWAR, Pakistan — A suicide bomber set off an explosives-laden vehicle on a field during a volleyball tournament today in northwest Pakistan, killing at least 32 people and wounding more than 70, police said.

The blast occurred near Pakistan's tribal belt, and was the latest bloodshed to rattle the country since the army launched a military offensive against Taliban fighters in the South Waziristan tribal region. The operation has scattered insurgents but provoked apparent reprisal attacks that have killed more than 500 people since October.

Police said today's bombing in Lakki Marwat city, not far from South Waziristan, was possible retaliation for local residents' efforts to keep militants out of the area.

"The locality has been a hub of militants. Locals set up a militia and expelled the militants from this area. This attack seems to be reaction to their expulsion," local police Chief Ayub Khan told reporters.

He said the bomber drove a vehicle loaded with 550 pounds of high-intensity explosives onto the field in a congested neighborhood during the volleyball contest.