Officials say twin bomb attacks against Pakistan Navy buses taking employees to work have killed four people and wounded more than 50 others in the country's biggest city.
Police say the blasts early today took place roughly 15 minutes apart in different areas of Karachi.
No one has claimed responsibility for the attacks.
Officials said the blasts were most likely remote-controlled bombs.
Karachi, the country's commercial hub, has a long history of bloody feuds between rival ethnic, political, and sectarian groups, in which hundreds of people have been killed.
The Taliban and other Islamist extremists carry out nearly daily attacks on security forces in Pakistan, mainly in the northwest, but correspondents say attacks on security personnel are rare in Karachi.
compiled from agency reports