A car bomb outside a fast food restaurant in the southern Pakistan city of Karachi has killed at least three people and injured about 15 others, some critically. A police official called the bombing an act of terrorism, but the target was not clear.

Police say the powerful bomb went off Tuesday morning outside a popular KFC outlet in downtown Karachi, gutting the restaurant and shattering windows in a nearby office block housing several oil and gas companies.

Initial suspicion was that the American fast food chain was the target. However, separatists from the southern Pakistan province of Baluchistan have claimed responsibility.

The separatists are demanding greater control over local resources, including oil and gas, and have claimed responsibility for several small bombings, mostly in southwestern Baluchistan, in recent years.

The Karachi police chief, Mushtaq Shah, says officials have launched a major investigation.

"It was a huge, huge explosion," said Mushtaq Shah. "We have collected all the available evidence from the scene and we're are working on that."

Mr. Shah says at least five kilograms of explosives were hidden inside a car, which was parked near the KFC restaurant in one of Karachi's busiest commercial districts.

Although officials did not say the restaurant was the target, other U.S. and Western interests have been attacked recently in Karachi.

In September bomb blasts targeted a KFC and a McDonalds. The attacks were allegedly tied to a militant Muslim group opposed to the Pakistan government's ties with the United States.

A KFC outlet was also set on fire earlier this year during violent clashes between Sunni and Shiite Muslim extremists. Six employees died.

Pakistani officials say there is no evidence linking Tuesday's blast with those earlier attacks, or a fresh wave of violence in neighboring Afghanistan.

Police there are blaming al-Qaida linked militants for two suicide bomb attacks against NATO peacekeepers on Monday.

The twin blasts killed at least eight people in the capital city, Kabul.