No one has claimed responsibility for the attack, but targeted killings have become increasingly common this year in Kandahar.
At least 27 people - all of them government officials or Afghan employees of foreign contractors - were assassinated in the first four months of 2010.
That trend has continued over the summer, most notably with the June assassination of Haji Abdul Jabar, the governor of Arghandab district north of Kandahar.
US officials have repeatedly delayed plans for a major military offensive in Kandahar.
Karzai adviser targeted
Meanwhile, in Nangarhar province, a bomb attack wounded Waheedullah Sabawoon, a senior adviser to Hamid Karzai, the Afghan president.
The bomb was hidden in a rickshaw, which exploded close to his vehicle.
Sabawoon was in the province on a personal visit. He was airlifted back to Kabul for medical treatment, according to the Kabul-based Pajhwok news agency.
His wounds were "not critical," Ahmad Zia Abdulzai, a provincial spokesman, said.
Sabawoon has worked as Karzai's tribal affairs adviser for more than four years. He once worked for Gulbuddin Hekmatyar, a former mujahideen commander and the leader of one of Afghanistan's three main insurgent groups.