The death toll in twin explosions caused by a spark in a munitions cache at an anti-terror police station in Swat rose to 17 on Tuesday, reported 24NewsHDTV channel.
The dead included 12 policemen and four inmates including a woman and a little girl being held at the Counter Terrorism Department (CTD) centre in Kabal area of Swat Valley. As many as 70 people including female police officers were also injured in the blasts.
CTD DIG Khalid Sohail said that the condition of eight officers was serious as the explosions levelled the specialist counter-terrorism station in Kabal.
Police sources said the back-to-back explosion have razed the building and the death toll is feared to go up further as rescue and cleaning operation was still under way on Tuesday.
The incident came amid a string of high-toll militant assaults on police across the country, many linked to the domestic Taliban branch, and initially sparked fears of a fresh attack.
But the head of Swat police said a short-circuit in a basement storing "grenades and other explosives" was the cause of the blasts. "There is no suggestion that it was caused by an outside attack or by suicide bombers," Shafi Ullah Gandapur told reporters.
Khalid Sohail, a senior officer in the local counter-terrorism department, said the shock waves caused "the complete collapse of the building".
"A series of two to three bomb explosions occurred," Akhtar Hayat Gandapur, the inspector general of Khyber Pakhtunkhwa police, told AFP, adding the "majority of the victims" were policemen.
Footage from the site showed a body being stretchered from the rubble as a smattering of small fires blazed in the darkness.
Bilal Faizi, spokesman for Khyber Pakhtunkhwa's rescue service, said 17 people were killed and 70 injured.
The Namaz-i-Janaza of nine of the 12 martyred policemen was offered at Kabal Police Lines on Tuesday, which was attended by KP IGP, police officers and a large number of locals.
After the funeral prayers, the bodies have been sent to the native towns of the martyrs.
- Police on edge -
Since the start of the year, two attacks on large police bases have been linked to the Pakistani Taliban, known as Tehreek-e-Taliban Pakistan (TTP).
On Twitter, Prime Minister Shehbaz Sharif initially described Monday's blasts as a "suicide attack".
"Our police has been the first line of defence against terrorism," he tweeted.
Late at night he tweeted an update saying "The nature of the blast is being investigated".
In January, a suicide bomber detonated his vest in a mosque inside a police compound in Peshawar, killing more than 80 officers as the building collapsed and rained down rubble on worshippers.
The following month, five were killed when a TTP suicide squad stormed a police compound in Karachi, prompting an hours-long shootout.
The TTP have long targeted law enforcement officials, who they accuse of conducting extrajudicial executions.
Pakistan has witnessed a dramatic uptick in attacks since the Taliban seized control of Kabul, focussed in its border regions with Afghanistan, and Islamabad says offensives are being launched from Afghan soil.
The TTP was founded in 2007, when Pakistani militants fighting alongside the Taliban in Afghanistan splintered off to focus attacks on Islamabad as payback for supporting the US invasion after the 9/11 attacks.
Reporter Khawaja Subhan