A suicide bomber targeted a police official in Pakistan's financial capital Karachi on Thursday, killing at least three people and wounding 13 others, police said.

Senior police official Rao Anwar said he was the target and claimed to have been threatened for a month by "unknown terrorists".

"The attack was against me. I was moving with my squad in Malir Halt district when the explosion took place. I am unhurt, but some of my men have been injured," Rao Anwar told AFP.

Police official Tahir Naveed told AFP it was a suicide attack.

Karachi is Pakistan's largest city and its port has been a lifeline for US troops fighting the Taliban in landlocked Afghanistan, though Pakistan shut down the supply lines last November when US air strikes killed 24 soldiers.

All of the dead were men and police suspect one of the bodies may be the bomber. Two teenagers were among the wounded.

The bomber struck near a bank in a garrison area of the sprawling city, which is home to 18 million people.

This week, Pakistan's human rights commission said ethnic, sectarian and politically linked violence had killed at least 300 people so far this year in Karachi, where migration has turned the city into a melting pot of different people.

The last bomb attack in the city killed three soldiers on December 9.