A bomb blast hit a police van in Karachi Friday, killing at least two policemen and wounding 14 other people, officials said, the latest violence in Pakistan’s strife-torn biggest city.

A bomb blast hit a police van in Karachi Friday, killing at least two policemen and wounding 14 other people, officials said, the latest violence in Pakistan's strife-torn biggest city.

"Two policemen were killed and 14 other people including two civilians were injured when a bomb planted on a motorbike was blown up as a police van was passing by," Karachi police chief Ghulam Qadir Thebo told AFP.

He said the officers belonged to the Special Service Unit, an elite squad that guards VIPs, and were on their way to guard Bilawal House, the residence of former president Asif Ali Zardari.

Nobody has claimed responsibility for the blast but militants linked to the Taliban and Al-Qaeda terrorist groups have attacked police vehicles in the city in the past.

Karachi, Pakistan's economic heart and home to 18 million people, is rife with criminal and political killings, which claim hundreds of lives each year.

Security forces have been cracking down on criminal and militant activities since late 2013, suffering reprisal attacks in return.