A bomber has attacked a site where a volleyball game was being played in northwest Pakistan, killing at least 88 people and wounding scores more, sources say.

The incident took place in Lakki Marwat in the North West Frontier Province, which lies close to North and South Waziristan.

The bomber apparently drove his vehicle onto a field where a volleyball tournament was under way.

"There was a match between two village teams and a lot of people were watching it," Habibullah Khan, the police chief of Bannu district, said.

Since the Pakistani army launched a ground offensive in South Waziristan in October, bombings have plagued Pakistan and killed more than 500 people.

Possible retaliation

Imran Khan, Al Jazeera's correspondent in the capital Islamabad, said: "Lakki Marwat is a place that has seen fighting against Taliban and al-Qaeda elements.

"The people of that area formed tribal militias to fight foreign fighters and the Taliban to push them out. So this was probably a retaliatory attack."

He said the bomber drove a vehicle loaded with 250kg of high-intensity explosives onto the field, which lies in a congested neighbourhood, during the volleyball contest.

Some nearby houses collapsed, and "we fear that some 10 or so people might have been trapped in the rubble", he said.

In addition, a group of local tribal elders were holding a meeting at a mosque nearby. The mosque was damaged and some people there died, he said.

Drone raid

Earlier on Friday, missiles fired by a US drone killed at least three anti-government fighters in North Waziristan, security officials said.

The attack took place early morning in Ghundikala village near the town of Mir Ali.

Another US drone attack late on Thursday killed at least three fighters when two missiles hit their hideout.

The use of so-called Unmanned Aerial Vehicles (UAVs), which allow the military to operate in highly dangerous areas, is expected to grow in the coming years with the US defence department expected to buy 700 drones next year alone.

Karachi shutdown

Against this backdrop of continued violence, Karachi, the country's largest city, came to a virtual standstill on Friday.

PHOTO CAPTION

A Pakistani paramedic gives treatment to an injured suicide blast victim at a hospital in Bannu late on January 1. 2010.

Al-Jazeera