Reuters quoted from security officials saying: "A car bomb blasted in Kabul targeting a foreign aid group."
Security perimeter was intensified around Kabul since Taliban fighters have announced their annual offensive in the spring, and the group vowed to target Afghan and foreign government facilities.
Interior Ministry spokesman Nasrat Rahimi said the explosion took place in Shahrenu area of Kabul, but had no details of the casualties.
Rahimi added that there was sporadic gunfire in the area.
One of the witnesses, Qais Zaman, said the blast site was close to the Attorney General's Office, and the area was cordoned off while ambulances and police vehicles rushed to the scene.
The blast came just over two weeks after gunmen targeted the Communications Ministry in central Kabul, and resulted in killing at least seven people. Furthermore, Daesh mercenaries have announced the adoption of this attack.