Pakistani police and paramilitary officers remove a dead body after a bomb blast outside a Kentucky Fried Chicken restaurant in Karachi

Police in the Pakistani port city of Karachi say a car bomb explosion outside an American fast food restaurant has killed at least three people and injured about 15 others.

The bomb set fire to the KFC restaurant and shattered windows in nearby offices housing several oil and gas companies early Tuesday.

Police initially thought the restaurant was the target. But a little-known separatist Baluch group claimed responsibility, saying it was targeting a state-owned oil company office housed above the restaurant.

Karachi police chief Mushtaq Shah said authorities have begun an investigation. He said at least five kilograms of explosives were hidden inside the car.

Karachi -- Pakistan's largest city -- has been the scene of political, religious and ethnic violence for years. Lately, police have also blamed violence on Islamic militants linked to the al-Qaida terrorist group.