Four suspects involved in the remote controlled blast in Lower Dir's area of Samar Bagh were arrested by security forces on Wednesday.
Unidentified militants killed four people in the Samar Bagh blast. During a search operation, police arrested four suspects, of which three are from that area and one from Afghanistan.
One kalashinkov, an army uniform and 75 expolsives have been seized from the suspects' possession.
The suspects have been sent to an undisclosed location place for further investigation.
The Lower Dir district, 200 kilometres from the capital Islamabad, borders Pakistan’s semi-autonomous tribal belt on the Afghan border, which Washington calls al Qaeda’s global headquarters.
Nearly 4,700 people have been killed across Pakistan in attacks blamed on Taliban and al Qaeda-linked networks based in the tribal belt since government troops stormed a radical mosque in Islamabad in 2007.