At least three people have been killed and 15 others wounded after a car bomb struck a fast-food restaurant in Karachi, southern Pakistan.
Police said the blast ripped through the front of a Kentucky Fried Chicken outlet and burned several vehicles.
The bomb exploded in a crowded business area near two luxury hotels at 0840 (0340 GMT), during rush hour.
It is not clear who carried out the attack. Previous Karachi bombings have been blamed on religious extremists.
Interior Minister Aftab Sherpao told the BBC that they are checking a claim by Baloch nationalists that the target was Pakistan's main petroleum company which has offices in the building.
Earlier, Karachi police chief Mushtaq Shah told journalists the bomb was hidden in a car parked outside the restaurant.
"It was a high-intensity explosion and its noise was heard in several parts of the city," he said.
"It appears that the KFC was the target."
He said it was detonated by remote control.
According to officials, police are making progress tracing the vehicle.
Two guards were killed, and one person died later of injuries sustained in the blast. The authorities say five people remain in a critical condition.
Office worker Muhammad Ramzan was stepping off a bus when the blast occurred.
"I suddenly heard a loud explosion and I sat on the ground," he told the AFP news agency. "There was smoke rising everywhere."
Local ambulance workers initially said six people had been killed, but police and government spokesmen cast doubt on that figure.
"Probably the volunteers took injured, unconscious people [for] dead," senior police officer Manzoor Mughal told AFP at the scene of the blast.
A spokesman for the extremist Balochistan Liberation Army (BLA) said they carried out the attack on the building as it houses the main offices of Pakistan Petroleum Ltd.
The company runs the largest gas field in Balochistan.
People there accuse the government of stealing their resources.
The BBC's Barbara Plett in Islamabad says the authorities are sceptical about the claim as it is unusual for the BLA to carry out attacks outside Balochistan.
Interior Minister Aftab Sherpao told the BBC that the government was investigating the claim and that he did not want to comment yet on its validity.
Plagued by violence
In September, several people were wounded when a Kentucky Fried Chicken and a McDonald's restaurant were bombed.
In May, six people were killed when protesters set fire to a KFC outlet in the city, during clashes between religious groups.
Tuesday's blast comes as a court in Karachi was due to hear an appeal against the death sentence for Ahmed Omar Saeed Sheikh, who was convicted of the kidnapping and murder of US journalist Daniel Pearl.
Over the last decade Karachi has been plagued by a mixture of sectarian, criminal and ethnic violence.