According to district police officer Swat, two children also sustained injuries in the blast.
Soon after the blast, police arrived at the site and the injured were shifted to a nearby hospital.
Meanwhile, at least 5kg of explosives were also seized in Mangalwar area of Swat by the security forces.
The Swat Valley was under the de facto control of Taliban commander Maulana Fazlullah from 2007 to 2009, where it imposed a harsh brand of Sharia law and carried out public floggings and hangings.
The militants were driven out by an army operation after a ceasefire broke down but remain a threat in the region.
Taliban insurgents shot girls' education campaigner Malala Yousafzai in the head in the valley in 2012.
Fazlullah, who says he ordered the shooting, was appointed chief of the Taliban in 2013.
Pakistan has been battling a homegrown Islamist insurgency for more than a decade after it agreed to cooperate with US-led NATO forces in their war in neighbouring Afghanistan.
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