A powerful explosion has rocked Pakistan's southern port of Karachi, killing at least one person and injuring two slightly.

A bomb, apparently hidden on a motorcycle, exploded near the headquarters of Pakistan State Oil, shattering windows.

We are investigating and trying to determine who was behind this bomb explosion Deputy police chief Tariq Jamil

It is not clear if the company was the target of the attack.

Police said no group had claimed responsibility for the blast.

"We are investigating and trying to determine who was behind this bomb explosion," said deputy police chief Tariq Jamil.

Sindh province's inspector-general of police, Syed Kamal, said a foreign group could be to blame for the blast, but it would be premature to point the finger at al-Qaeda.

"We cannot rule out foreign hand in the blast," he said.

He identified the dead man as Pujabi Karim Dad. One of the injured was a policeman, the inspector-general said.

Police and paramilitary units have set up road blocks in surrounding streets.

Violent history

The person killed in the blast was apparently the rider of the motorcycle, a Pakistan State Oil executive told the BBC.

The two injured people sustained cuts and bruises but were able to walk away from the scene, he said.

At least one person was killed in the blast

Vehicles in the area were severely damaged by the blast.

State Oil company's executive in charge of health and safety said the blast was not necessarily connected to his company, as the parking lot served other buildings and shops in the area.

Two years ago, the head of Pakistan State Oil died in a sectarian attack carried out by militants from Pakistan's Sunni Muslim majority, but the executive said this latest attack was almost certainly not connected to that killing.

Recent bombings

Karachi has been the scene of a series of bombings and other attacks in recent months.

A suicide bomber killed 11 French engineers and two Pakistanis in the city last May.

The engineers had been working with the Pakistani Navy on a submarine project.

In June, a car bomb at the US consulate in Karachi killed 12 and injured 50.

Police have arrested suspected Islamic extremists in connection with both bombings.