Four policemen were among those killed in market place bombing in the garrison city of Bannu, army spokesman Major General Waheed Arashad said.

Around 20 people were injured in the blast and many of them are stated to in a critical condition, officials said.

The bomber was travelling in an auto-rickshaw and detonated the explosives in a crowded place near a police van, they said.

The burqa-clad bomber set off the explosives when the police tried to intercept the vehicle, Interior Ministry spokesman Javed Iqbal Cheema said, adding it was not known whether the attacker was a woman or a man.

The army spokesman denied reports that a convoy of security forces was the target.

"It was a suicide attack. It was not targeted at any military convoy," he said.