Zalmai Oriakhil, Kabul deputy police chief, said the shooting led hundreds of people to mob soldiers before Afghan elders and police intervened.
Nato and the US-led coalition could not confirm the shooting.
The bomber, who died in the attack, planted the explosives in a taxi, the Afghan interior ministry said in a statement.
"I was driving. The car just behind me exploded. It was a terrible explosion," one witness said.
|Isaf troops are facing increasing |
attacks in Afghanistan[AFP]
"An Isaf convoy was coming from the opposite direction. An Isaf vehicle was on fire but drove away," he added.
The attack was the fifth suicide bombing in the capital this year but there have been several others around the country, mainly in the south and east.
The attack in Mazar-i-Sharif targeting a US military convoy came hours after the blast in Kabul.
It missed the US convoy, which sped off, said Abdul Rauf Taj, the provincial head of security and police.
"One person was killed and six injured," he said. The casualties were all civilians and the wounded included a woman and a child, Taj said.