According to the message, sticky bomb was attached to one of the vehicles.
Four people were in the vehicle at the moment of explosion, three of them died.
"The victims of the Saturday attack are two female government employees from the water supply department and a small child," agency reports, according to the spokesman.
The driver was also wounded.
No terrorist group has claimed responsibility for the attack as of yet.
Earlier US intelligence predicted deterioration of situation in Afghanistan this year and strengthening of "Taliban" positions.