A suicide bomber on a motorbike killed at least four people and wounded several others in Kabul, Afghanistan, in an attack on a vehicle carrying national security officials, according to a security official at the scene in the Afghan capital.

An interior ministry official confirmed the attack but could not say immediately how many people were killed or wounded.

According to the ministry’s spokesman, Najib Danish, the suicide bomber blew himself up in the Pul Mahmood Khan area. The target is unclear.

There was no immediate claim of responsibility for the attack.