The attacker targeted JUI leader Mufti Syed Janan, who is contesting polls to the Khyber-Pakhtunkhwa assembly, in a market at Doaba in Hangu district.
Janan, who was meeting traders as part of his campaign, escaped unhurt.
At least a dozen people were killed and some 40 others injured by the powerful explosion, officials and witnesses said.
Witnesses said they had seen several bodies and injured persons lying at the site. The injured were taken to hospitals at Doaba, Hangu and Thal.
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No group claimed responsibility for the attack, which came a day after 24 people were killed in a bombing at an election meeting organised by JUI leader Munir Orakzai in Kurram tribal region.
The banned Pakistani Taliban claimed that attack.
Pakistan has witnessed a spike in violence ahead of the May 11 general election.
The Tehrik-e-Taliban has vowed to target secular parties like the Pakistan People's Party and Awami National Party.