"I thought it was an earthquake," security guard Hassan Ali, being treated in hospital for head injuries and bandaged over his left eye, told Reuters. He said he had passed out during the blast.

Provincial authorities said they suspected Islamist militants might be to blame and cast doubt on a claim of responsibility by a separatist group from nearby Baluchistan province which said it had targeted an office of a state-run Pakistani oil company.

"Indications are that extremist and militant organizations could be involved in the blast. The blast got instant publicity the world over and that's what the militants want," Salahuddin Haider, spokesman for the Sindh provincial government in Karachi, told Reuters.

A small Suzuki sedan blew up just before 9 a.m. (0400 GMT), gutting the restaurant on the ground floor of the six-story office block and shattering all the windows in the building which houses several oil and gas exploration firms, including Pakistan Petroleum (PPL) which runs Pakistan's largest gas field in Baluchistan.

Manzoor Mughal, a senior police investigator, told The Associated Press that one foreign national of unknown nationality was among the injured, but was released from a hospital after being treated.

Police said they had found some clues on closed circuit TV cameras mounted on the Pakistan Industrial Development Corp. building, which houses the KFC outlet and is also near two luxury hotels and the home of Sindh province's chief minister. England's touring cricket team is due to stay in the area next month.

Doctors said six people had been admitted to hospital in a critical condition, some with severe burns. The materials used, 5 kg (11 lb) of military-style RDX explosive and gunpowder, made the blast particularly intense, police told Reuters.

President Pervez Musharraf ordered a crackdown in July on militant groups, particularly those fueling hatred between Pakistan's majority Sunni Muslims and minority Shi'ites.

In September, two nearly simultaneous explosions went off at other fast food restaurants -- another KFC and a McDonald's in Karachi's Defense district.

U.S. fast food outlets in Karachi have been targeted before. On May 30, a KFC restaurant was burned and six workers inside were killed during an outbreak of religious sectarian violence in the city.

England's cricket team is due to play a one-day international in Karachi on December 15. The tourists only agreed to play there after much persuasion from Pakistan's cricket authorities.

In May 2002, New Zealand's cricket team flew home without playing a test after a suicide bomb attack on a bus outside its Karachi hotel. That blast killed 11 French naval technicians.

Copyright 2005 CNN. All rights reserved.This material may not be published, broadcast, rewritten, or redistributed. Associated Press contributed to this report.

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