Two people were killed and 15 others wounded when a bomb exploded near a local party office in Pakistan's Karachi late Tuesday, officials said, the latest attack ahead of historic polls next month.

Police officer Imran Shaukat said two men riding a motorcycle threw the bomb close to the office of the secular Muttahida Qaumi Movement (MQM), causing the dead and injured.

MQM was a coalition partner in the recent government and has been threatened by Pakistan's umbrella Taliban faction.

Party spokesman Wasey Jalil told AFP: "It was an improvised explosive device and the target was our party. It was hurled when MQM workers were erecting a party flag at a nearby electricity pole."

"Two of our workers were killed and three wounded." He added that the other victims were ordinary commuters who had been waiting at a bus stop.

Taliban threats and bomb attacks have overshadowed much of Pakistan's election campaign.

The Pakistani Taliban have threatened three main secular parties in the outgoing government -- the Awami National Party, the Pakistan People's Party and the MQM.

Deadly attacks targeting politicians or political parties have killed 26 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.