The death toll in a roadside bomb attack targeting troops in Pakistan's port city of Karachi has risen to two, officials said Friday.

The blast was aimed at soldiers returning to their barracks by truck after carrying out security duties at polling stations for by-elections in the city on Thursday.

"An army soldier, who had sustained injuries in the attack died overnight of wounds, rising the toll in the attack to two," a senior security official told AFP.

The official who did not want to be named said the condition of 10 other soldiers wounded in the attack was stable.

A local intelligence official also confirmed the new toll.

The attack initially killed a civilian and left 16 more people including 11 soldiers wounded in the violence-plagued port city.

A bloody wave of killings and kidnappings has hit Karachi, a sprawling metropolis of 18 million people on the Arabian Sea and Pakistan's economic heart.

Bloody gang wars fed by ethnic and political bitterness, drugs and the Taliban, have created a culture of impunity, and the past two years have seen record death tolls.

In the first six months of 2013, 1,726 people were killed in Karachi compared with a previous high of 1,215 in the same period last year, according to the Human Rights Commission of Pakistan.