Three men and a woman are being sought over the murder of an 11-year-old boy who was allegedly strangled to stop him from wedding one of the killers' women in an arranged marriage.

The marriage had been ordered in compensation for the kidnapping of the boy's 15-year-old sister. Mohammad Asif was killed on Sunday, five months after his sister was abducted from their home.

The children's widower father, Saeed Akbar, a rickshaw driver, appealed to a tribal jirga, or council, for justice after his daughter was snatched. But after the jirga ordered the kidnappers to betroth one of their daughters to the boy, they began making threats, prompting Akbar to seek protection from the jirga.

"But before that they killed my innocent son in revenge," he said, describing how he saw smoke rising from his house after leaving for work.

"I rushed back and found the house was on fire. I called for help and we took out Asif's dead body," he told Dawn Newspaper.

A post-mortem showed the boy was strangled and his body burned afterwards.