Around 40 others were injured in the attack in the centre of the provincial capital, also called Kunduz, said Mahboobullah Sayedi, spokesman for the province's governor.
Most of the victims were volunteers who had queued up near the centre to enrol with the national army, he said.
A DPA reporter said the blast was followed by the sound of gunfire. The bombing came four days after a suicide bomber killed provincial police Abdul chief Rahman Sayedkhili and four others in the centre of the city. The attack also injured the deputy police chief.
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