An accidental explosion ripped through a store in northwestern Pakistan on Saturday, killing at least three people and trapping others in a separate building that caught fire, police said — rattling nerves in a city repeatedly pounded with militant attacks.

Officials initially said the blast in a commercial district of Peshawar was caused by a car bomb, but investigators found no trace of explosives at the scene. Police Chief Liaquat Ali Khan said it was an accidental explosion that went off in a shop with paint stored inside. The exact cause was still unclear.

The explosion damaged vehicles and shattered windows in a wide stretch along a major road. At least three people died and seven others were wounded, police official Gohar Zaman said.

Several people were seen clinging to windows and shouting for help in one building full of lawyer's offices that caught fire. Firefighters struggled to put out the flames, and some tried to get into the building using a ladder. City official Sahibzada Mohammad Anis estimated that dozens were trapped.

Peshawar has become a frequent target for anti-government, Islamist militants — so officials were quick to assume at first that Saturday's blast was another attack.

A wave of bombings and homicide assaults have killed hundreds and underscored the resilience of militant networks in Pakistan, which is waging an offensive against the Taliban along the Afghan border but faces U.S. pressure to do more in the war on Islamist extremism.

On Friday, a Taliban homicide squad killed 37 people at a mosque frequented by army personnel near the capital, including several senior officers.