A parade inside the Frontier Constabulary (FC) headquarters in Peshawar was the target of the suicide attack, sources said on Monday.
Nearly 450 personnel were present for the parade at the time of the coordinated suicide assault carried out at 8.10am, the sources added.
Three FC personnel were martyred in the attack carried out by Afghan nationals.
All attackers were killed in an effective response by the FC personnel, according to Khyber Pakhtunkhwa Inspector General of Police Zulfiqar Hameed.
A faction of the Tehreek-e-Taliban Pakistan (TTP), Jamaat-ul-Ahrar, claimed responsibility for the attack, saying it was executed by its suicide unit “Khulafa-e-Rashideen Ishtihadi Khandak.”
The sources said the three attackers approached the FC headquarters on foot, wearing suicide vests and appeared to be between 18 and 22 years old.
IG Hameed said FC personnel fought back bravely, killing two attackers in the gunfight, while the third detonated his explosives at the main gate. All three terrorists were neutralised.
Hospital officials confirmed that eight people were injured and shifted to Lady Reading Hospital, including four FC personnel and five civilians.
The martyred personnel were identified as Havaldar Alamzeb Khan, Constable Riasat Khan and Constable Altaf Khan of platoons 277 and 478.
Among the injured were Lance Naik Zahir, Constable Arshad, Constable Riasat Khan, Constable Irfan Khan and a civilian tailor, Amjad Khan.
Officials said all injured were in stable condition and emergency protocols had been activated at LRH.
Residents reported continuous gunfire from the direction of the FC headquarters after the blast as police and security forces sealed off the area.
Rescue teams, the bomb disposal unit and a large contingent of police remained engaged in a clearance operation.
The BRT service was temporarily suspended as a precaution for passenger safety, but was later restored.
Police officials said the attackers intended to infiltrate the FC headquarters and cause mass casualties, but the swift response of FC personnel prevented a bigger tragedy.