The bomber blew himself up in Kohat, home to at least half a million people and one of the main garrisons for the Pakistan military, in the northwestern province of Khyber Pakhtunkhwa.

“It was a suicide blast. The death toll has risen to 17,” Kohat police chief Dilawar Bangash told AFP, adding that 25 others were wounded, seven of them seriously.  (Death toll has risen to 19: DawnNews)

Police said the bomber blew himself up at the door of a bus carrying passengers to the nearby tribal district of Orakzai, where Pakistan has encouraged displaced civilians to return after an anti-Taliban offensive.

“We have found the head and legs of the suicide bomber,” said Bangash. The bus terminal is in Tirah bazaar, the main market in the town.

The attack coincided with the start of Muharram, which traditionally sees tensions rise between Pakistan's majority Sunni Muslim and minority Shia Muslim community.

But police said the target was not immediately clear.

“It is true there were more Shias killed in the attack but there were a number of Sunnis also who died in the blast. So we cannot say who was the target,” said Bangash, adding the suicide bomber was aged 15 to 16.