Karachi, Pakistan - A suicide bomber blew up his sport-utility vehicle in the middle of a village volleyball game in northwestern Pakistan on Friday afternoon, killing 75 people and injuring more than 100 in a community that has repeatedly defied Taliban extremists.

Police speculated that the horrific bombing in the village of Shah Hassan Khel, in the Lakki Marwat district, was an act of reprisal against area leaders who last year formed private militias to oppose the Taliban and recently turned in a group of extremist fighters to the authorities.

The attack was the latest in a string of terrorist bombings across Pakistan that have increasingly targeted civilians and killed more than 500 people since September. The Taliban has asserted responsibility for many of them but denied carrying out others.

The latest high-fatality attack took place Monday in the southern port city Karachi, where an explosion targeting a Shiite religious procession killed 44 people; on Friday, the city of 18 million people was virtually shut down in protest. An October bombing in a women's bazaar in Peshawar, in the northwest, left more then 80 people dead.

The northwestern region near the Afghan border and the tribal area of South Waziristan, where the Pakistani army has been carrying out operations against Taliban forces since October, has borne the brunt of the violence. Terrorists have struck markets, mosques and other crowded civilian targets there, but Friday's bombing was the first to single out a sporting event.

Several previous attacks were clearly carried out in retaliation against communities and leaders who resisted the Taliban. In November, a bombing in a rural market killed a local mayor who had openly defied the extremists. As more communities begin fighting back, there is concern that reprisal attacks will also increase.

The powerful explosion Friday left dead and wounded people, including women and children who had been watching the match, scattered across a playing field in the heart of the village. It also damaged houses and other buildings.

The area's remoteness caused delays in bringing the injured to hospitals, and the death toll rose all evening.

Anwar Kamal Marwat, a politician and tribal leader who organized anti-Taliban militias in the Lakki Marwat district, said by telephone from nearby Peshawar that the bombing was definitely intended to retaliate against the armed and organized villagers, who had recently arrested and turned in 24 Taliban members.

"They have been punished for their active role against the militants," Marwat said, noting that the Taliban influence had been growing in the village area before the local militias struck back.

The local police chief, Ayub Khan, echoed that assessment, telling the Associated Press that the bombing appeared to be a reaction to the "expulsion" of local Taliban fighters. He said the bomber's vehicle contained 500 pounds of high-intensity explosives, and that a second suicide vehicle may have escaped from the area.

The bombing took place as the latest airstrike by suspected U.S. drone planes struck a car carrying three suspected Taliban militants in North Waziristan. Another missile strike Thursday struck a house in the same region, killing three people, according to Pakistani officials.