KARACHI (AFP) - A powerful bomb exploded near the election office of a secular party in Pakistan's port city of Karachi late Friday, injuring 15 people, police said, the latest violence ahead of historic polls next month.

The bomb went off close to the campaign office of an Awami National Party's candidate in the city's western neighbourhood of Mominabad, local police officer Mohammad Khan said.

The nature of the bomb was not immediately clear. The blast was heard several kilometres away and damaged nearby shops and houses, witnesses said.

"The target was the election office of the ANP whose candidate Bashir Jan was to address a corner meeting" in the Pashtun dominated impoverished area, Mr Khan said.

Friday's blast was the second in the country's commercial hub of Karachi in less than 24 hours. Five people were killed on Thursday when a bomb exploded outside the office of secular Muttahida Qaumi Movement (MQM) party, police said.

The ANP and MQM were coalition partners in the outgoing Pakistan People's Party-led government and have been threatened by the Taleban. All three parties are perceived as secular.

Deadly attacks targeting politicians or political parties have killed 34 people since April 11, according to an AFP tally. May 11 national polls should see power pass from a civilian government that has served a full term to another through the ballot box for the first time in the nuclear-armed country's turbulent history.