Security around Kabul has been tight since Taliban militants announced their annual spring offensive and the group vowed to target Afghan government and foreign installations.
Interior Ministry spokesman Nasrat Rahimi said the blast was in the Shahr Naw area of Kabul, but he had no details on casualties.
Rahimi added there was sporadic gunfire in the area.
Qais Zaman, a witness, said the site of the explosion was close to the Attorney General’s office. The area was cordoned off as ambulances and police trucks rushed to the scene.
The blast comes just over two weeks after gunmen targeted the communications ministry in central Kabul, killing at least seven people. That attack was claimed by Islamic State.