| Pakistani boys search useful items from the rubble of damaged Kentucky Fried Chicken restaurant in Karachi |
Four of the victims were burned alive when the mob set fire to a crowded restaurant. Police say two others froze to death while they hid in the restaurant freezer.
Officials say all six were employees at the Kentucky Fried Chicken outlet, a U.S.-based fast food chain.
The riots occurred Monday evening after a suicide bomb attack at a Shi'ite mosque in eastern Karachi.
Police say three men led the attack. At least one of the men reportedly belonged to a Sunni militant group blamed for previous attacks against Shi'ite, Christian and government targets.
Senior police officer Mushtaq Shah says nearly a thousand protesters quickly flooded the surrounding streets after the explosion.
"The riots started soon after the bombing," he said. "About a dozen vehicles have been burned, five or six buses have been bombed, a KFC outlet has been bombed, a couple of gas stations…"
In a separate incident Monday evening unknown assailants in Karachi killed a popular Sunni Muslim cleric.
Aslam Mujahid was a senior member of Pakistan's largest Islamic group, Jamaat-e-Islami.
Monday's violence comes just three days after a suspected suicide bomb killed at least 19 and injured dozens more at a Shi'ite festival in Islamabad.
The government has strongly condemned all three incidents. Meanwhile, Mr. Shah says police in Karachi are bracing for a possible rise in sectarian violence.
"We've put the entire force on high alert and we have deployed our reserves on the streets at important points," he said.
Besides being Pakistan's largest city, Karachi is probably its most violent. Clashes between Sunni and Shi'ite militants are not uncommon.