The blast took place close to Pakistan´s border regions with Afghanistan, where Islamist militants are strong.[break]
The target of the attack in Kohat city was unclear, though insurgents have exploded bombs in public places before, presumably to spread terror and undermine confidence in the government.
The market is home to a bus stand where people were gathering to return home to the border region.
Shad Ali, a doctor who heads the health administration in Kohat, said 15 were killed and 25 injured.
Islamist militants seeking to overthrow Pakistan´s broadly pro-Western government have carried out scores of bombings in recent years, mostly against Western or government targets. The army has responded with offensives in some parts of the northwest.
On Monday, 50 people were killed in two blasts at a government compound in Mohmand, also in the border area.
A spokesman for the Pakistan Taliban, the main militant group in the northwest, claimed responsibility for that attack earlier Wednesday.
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