The spokesman, Nasrat Rahimi, said the bomb had gone off in a neighborhood which is near the interior ministry and north of Kabul airport.
He said the dead were all civilians. "This is the initial information, more details later," he added, according to AFP.
No one immediately claimed responsibility for the attack, but both the Taliban and Daesh (ISIL or ISIS) are active in the capital and have claimed many previous attacks in Kabul.
Ambulances sirens could be heard, and a giant plume of smoke rose from the area of the explosion.