A string of explosions rocked a police station in the northwestern Kabal town of Swat Valley, killing at least 12, but the police said they did not suspect a terrorist motive.
The explosion mostly killed policemen and leveled the special counter terrorism facility.
What we know about the blasts
The head of the Swat police was cited by the French AFP news agency as saying the explosions were caused by a short-circuit in a basement where "grenades and other explosives" were stored.
"There is no suggestion that it was caused by an outside attack or by suicide bombers," AFP quoted Shafi Ullah Gandapur as saying.
The regional chief of the counter-terrorism unit, Sohail Khalid also told reporters the explosion did not appear to be an act of terrorism.
"There was a store where we had a huge quantity of weapons, and until now we believe that there might have some blast in it due to some carelessness," the Reuters news agency quoted him as saying. "We are keeping all our options open."
PM backtracks on suicide attack claim
Monday's blasts were initially thought to be "suicide" attacks by Prime Minister Shehbaz Sharif earlier on Monday. He later tweeted that the nature of the blast was being investigated.
The region, which is close to the border area with Afghanistan, is prone to insurgency. It was the birthplace of Mullah Fazlullah, the former chief of the Pakistani Taliban, and also where militants shot and wounded Nobel Laureate Malala Yousafzai in 2012.
Two attacks targeting police bases have been linked to the Pakistani Taliban this year.