KARACHI (Reuters) - A car bomb exploded outside a KFC fast-food restaurant in the Pakistani city of Karachi on Tuesday, killing three people and wounding 15 in an attack thought to have been carried out by Islamist militants, police and doctors said.

Some victims suffered severe burns in the bombing, which blew a meter-wide (3-feet-wide) hole in the street and engulfed it in a fireball that gutted six or seven other parked cars in the center of the southern city, Pakistan's commercial hub.

"I thought it was an earthquake," said security guard Hassan Ali, being treated in hospital for head injuries and bandaged over his left eye. 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.

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

"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," said Salahuddin Haider, spokesman for the Sindh provincial government in Karachi.

Police said they had found some clues from security 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.

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