A suicide bomber blew himself up near the car of Jamiat Ulema-e-Islam leader Mufti Syed Janan while he was campaigning in a market at Doaba in Hangu district.
A dozen people were killed and nearly 40 injured, officials and witnesses said.
Janan, who is contesting polls to the Khyber-Pakhtunkhwa assembly, escaped unhurt. The attacker targeted Janan as he was meeting traders.
Witnesses said they had seen several bodies and injured persons lying at the site.
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Security forces cordoned off the area and launched a search operation.
Hours later, an explosion ripped through an election meeting organised by the Pakistan Peoples Party at Baba Gaam area of Lower Dir district.
State-run media reported three persons were killed and several others injured.
No group claimed responsibility for both attacks, 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.
President Asif Ali Zardari and caretaker Prime Minister Mir Hazar Khan Khoso condemned the attack on Janan.
Khoso directed authorities to further tighten security for candidates, public meetings, rallies and the people.
Zardari said such cowardly acts by militants could not deter the people from participating in the elections.
He said this would further strengthen the resolve of democratic forces.