One tribal policeman was among the dead and two others were injured.
"The bomb also destroyed two vehicles," Said Ahmad Jan, the official, said.
Militants opposed to the government, particularly the nebulous Tehreek-i-Taliban (TTP) network, have carried out bomb and gun attacks killing more than 4,700 people across Pakistan since July 2007.
Pakistan has for years battled insurgents in the tribal belt. More than 3,000 soldiers have died.
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