ISLAMABAD, May 15 (Xinhua) -- At least nine security personnel were killed and 21 others injured after a suicide bomber rammed an explosive-laden vehicle into a scouts camp in Pakistan's northwestern Khyber Pakhtunkhwa province on Thursday night, police sources said.

The explosion occurred at around 7:55 p.m. local time (1455 GMT) at the headquarters of the scouts in Bajaur district, the sources told Xinhua on condition of anonymity.

According to preliminary information from the sources, the explosive-laden vehicle approached the main gate of the compound and detonated after security personnel attempted to stop it, damaging the gate and surrounding walls.

"Following the blast, heavily armed militants opened fire using small and medium weapons, triggering an exchange of fire with security forces stationed inside the headquarters," the sources added.

After the firing subsided, rescue and clearance operations were launched inside the compound. Authorities said the process of identifying the dead and injured was ongoing.

Several terrorists were also reportedly killed during the exchange of fire, while authorities were verifying the exact number of militant casualties, the sources said.

The nature and extent of the damage were still being assessed as security forces continued operations in the area.

The injured troops were shifted to a nearby hospital.

No group has claimed responsibility for the attack yet. ■