Pakistan says it has killed a rebel tribal leader during a combat operation in the southwestern province of Baluchistan.  The tribal leader's death has sparked has widespread riots in the provincial capital, Quetta

Armed police in vehicles patrolling streets in Quetta, August 27, 2006

The government has imposed a 24-hour curfew in the city of Quetta, to put down violence that erupted Saturday almost immediately after news of Nawab Akbar Bugti's death became public.

Hundreds of Bugti's supporters rioted throughout the night. At least a dozen buses and other vehicles were torched near the local university, and piles of burning tires blocked a number of key city roads.

Bugti, once governor of Baluchistan province, was a central figure in a violent campaign to secure greater control over the province's resources, including valuable natural gas deposits.

The central government calls him a terrorist, and accuses his supporters of targeting government outposts and destroying local infrastructure, including natural gas pipelines.

Interior Minister Aftab Sherpao says security forces attacked Bugti's mountain hideout Saturday, after government helicopters came under heavy fire from an isolated cave.

"It is presumed that Akbar Bugti and a number of other terrorists were occupying this cave, and they are presumed dead," said Sherpao.

Government officials say more than 20 militants were killed in the strike.

Sherpao says the operation was a significant victory for the government and its campaign against tribal militants in the area.

But there is concern that Bugti's death could cause more, not less, tribal resistance.

Opposition political leader Raza Rabbani says the government has been too quick to use the military to try to resolve what is largely a political conflict.

"The people of Baluchistan feel that their economic and political rights have been deprived," he said. "By using state force, all that we have done is further alienate Baluchistan."

The government launched its latest offensive against Bugti last December, after tribal militants fired rockets at President Pervez Musharraf during an official visit to Baluchistan.

The Pakistani military has been placed on high alert throughout the country to prevent any further unrest connected to Bugti's death.