Most of those caught in the blast were passersby
A suicide bomber has killed at least 16 other people at a checkpoint in a market in north-west Pakistan.
More than 20 people were also injured when the bomber, on foot, detonated at a bazaar in Khar, the main town in the troubled Bajaur tribal region.
Only last year, Pakistan's military declared victory over militants in the district, following a ground offensive.
Meanwhile, nine militants died in a US drone air strike in North Waziristan, local officials said.
In Saturday's suicide blast, the bomber is said to have been heading for government buildings and military barracks when he was stopped by soldiers.
The troops were carrying out a body search when the attacker detonated an explosives-packed vest, Iqbal Khattak, a government official, told AFP news agency.
"The death toll has gone up to 16, including two paramilitary soldiers," Mr Khattak said.
Several vehicles and four shops were destroyed in the bombing, he added.
The suicide attack came a day after Pakistani security forces killed at least 24 suspected militants in air strikes and clashes in Bajaur.
In February 2009, the army said Bajaur had been cleared of Taliban militants following a military operation launched in August the previous year. But recently the security situation has been deteriorating.
The BBC's Aleem Maqbool in Islamabad says numerous attacks over the last six months show the militants still maintain a significant presence in the area.
Close to the Afghan border, Bajaur has long been suspected of being the hiding-place of Osama Bin Laden, Ayman al-Zawahiri and other top al-Qaeda leaders.
Pakistan's military has been focusing on a major offensive, launched in October, nearby throughout the Taliban stronghold of South Waziristan.
But some analysts say that military operation has simply displaced militants to other parts of the tribal belt.