The casualties include training centre members, police personnel and civilians. The toll might increase further, the official told Xinhua news agency.
The attack took place in the provincial capital of Gardez city, 100km south of Kabul, reports Xinhua news agency.
The number of attackers was six, all equipped with suicide vests and light arms, according to security forces.
No group has so far claimed responsibility for the attack.
This post was last modified on October 17, 2017, 2:17 pm