The Interior Ministry says five police officers, including a district police chief, have been suspended over Tuesday's blast in Kabul and are under investigation for neglecting their duties.
No one has claimed responsibility for the blast.
Roadside bombings are a major threat for both security forces and civilians across Afghanistan, where the Taliban have been waging a 15-year war against the government and foreign troops.
Afghanistan's police are widely seen as incapable and corrupt, and are often implicated in crimes such as kidnapping for ransom, which has become widespread as the economy has shrunk and unemployment has risen above 25 per cent.