At least 14 people have been killed in a Pakistan bombing which militants say was in revenge for the execution of a policeman turned assassin.

The suicide attack, at the entrance to a court in the north-western town of Shabqadar, wounded nearly 30 others, police told local media.

Militants said it was to avenge the hanging last week of Mumtaz Qadri, who was seen by many as a religious hero.

Qadri killed the governor of Punjab in 2011 for opposing blasphemy laws.

Shabqadar is located on the border of the tribal district of Mohmand, which remains volatile years after the military said it had been cleared of militants.

"The court and judges were our target as their practices are un-Islamic," a spokesperson for Jamaat-ul-Ahrar, a splinter group of Tehrik-e Taliban Pakistan (TTP), told Pakistan's Express Tribune.