A parcel bomb exploded Tuesday at a checkpoint in the port area of the southern Pakistani city of Karachi (search), killing at least two people and injuring five, police and an emergency worker said.

Police officer Raja Azhar said a man approached a checkpoint at a shipping yard of the state-run Karachi Port Trust (search) and handed a parcel to a security official deployed there. The parcel exploded soon thereafter.

Rizwan Edhim, spokesman for the emergency relief agency Edhi Foundation (search), said two people were killed and five were wounded.

Police officer Ather Rasheed Butt said the blast was caused by a small bomb. Five people were hospitalized, including two in serious condition. He could not confirm any deaths.

There was no immediate claim of responsibility for the bombing.

Authorities kept a reporter away from the scene.

Karachi, Pakistan's biggest city and its main port, has been a target of bombings and terror attacks in the past.

This past week, police arrested seven militants from an extremist Islamic group blamed for an assassination plot on President Gen. Pervez Musharraf (search) in April 2002 and a bombing outside the U.S. Consulate in Karachi that killed 12 people in June 2002.

They also seized bomb-making materials and weapons, and police said the suspects were planning further terror attacks.

A May 7 suicide bombing on a Shiite Muslim mosque killed 15 people. Authorities suspected radical Sunni Muslims were behind that attack.