A suicide bomber targeted the humanitarian organisation in the Shar-e-Naw area and gunmen then stormed the building, Tolo News TV reported.
The explosion has rocked the centre of the Afghan capital Kabul, and reports say gunmen have attacked the offices of a charity.
The Taliban, who have carried out frequent attacks in Kabul, said they were responsible for the blasts.
One person had been killed and six others wounded in the suicide car bomb attack at the gate of the charity Care on Tuesday morning.
Police are exchanging fire with the attackers, the report added.
An army general and two senior police officers are among the dead from those attacks, a ministry of defence spokesperson told the Media.
Traffic was blocked in several parts of the city and schools were closed.
