A powerful car bomb exploded outside a KFC restaurant in southern Pakistan on Tuesday, setting off a massive fireball that overturned cars and shattered steel and glass. Three people were killed and 22 injured.

An ethnic Baluch nationalist group from southwestern Pakistan claimed responsibility. A spokesman denied the group targeted civilians, saying it tried to hit the offices of a state-owned oil and gas company above the KFC.

"We did it to protest, and we did it to pressure the government to get our rights," Chakar Azam, spokesman for the Baluchistan Liberation Army, said in a phone call to The Associated Press.

The powerful blast struck at about 8:45 a.m., as commuters were heading to shops and offices in the crowded downtown area of Karachi, Pakistan's business hub.

Mushtaq Shah, Karachi's police chief, told reporters the bomb was concealed in a car parked outside the restaurant. Doctors said two men died on the spot and a third died at a hospital.

Police explosives expert Mohammed Iqbal said the bomb was made from 11 pounds of homemade explosives and detonated by a timer. The car containing the bomb was blown to pieces, leaving a six-foot crater. Officers initially said the KFC restaurant, part of the global American fast food chain, was the target.

Manzoor Mughal, a senior police investigator, said the blast also damaged the offices of three Pakistani banks. One foreigner of unknown nationality was among the injured, but was released from a hospital after being treated, he said.

Azam said the BLA targeted state-owned Pakistan Petroleum Limited, which had offices in the floors above the KFC restaurant. The BLA demands more government aid to Baluchistan, where Pakistan's main natural gas fields are located.

The blast marked the first time the group has claimed responsibility for an attack outside Baluchistan province, where it has launched occasional bomb and rocket attacks against security forces, gas installations and other infrastructure.

Interior Minister Abtab Khan Sherpao told the private Geo television network the group's claims were being investigated.

Karachi has been the target of a number of bombings in recent months that have killed more than a dozen people. Police said they had tightened security in the city and were searching for clues about those behind the attack, including from security cameras installed near the bomb site.

Hundreds of people gathered at the bomb site in the area of government offices and luxury hotels. The blast was powerful enough to damage windowpanes at the Pearl Continental Hotel, which is popular with foreign tourists and businesspeople.

Karachi, Pakistan's largest city, is a center of Islamic militancy, and previous bombings in the city have been linked to extremists opposed to Pakistani President Gen. Pervez Musharraf's close ties to the United States.

Pakistan's information minister, Sheikh Rashid Ahmed, condemned the blast, calling it the work of the "enemies of Pakistan."

The attack came three days before Pakistan is to host a conference of international donors to raise funds for victims of the devastating Oct. 8 earthquake that killed about 86,000 people in the country's northwest and in Pakistani-controlled Kashmir. Hundreds of U.S. and other foreign troops are in the country helping with quake relief.

In September, bombs struck KFC and McDonald's restaurants in Karachi, injuring three people in attacks believed linked to a nationwide strike called by a hardline Islamic coalition opposed to Musharraf.

A KFC restaurant in Karachi also was burned in May, killing six workers inside during an outbreak of religious violence between Sunni and Shiite Muslim groups in the city.