Assailants killed four members of a family, including two children, and injured another with sharp weapons in Bhurangamari upazila of Kurigram.
Police reported that miscreants broke in late on Tuesday night and killed Sultan Mia, 55, Hazera Begum and their granddaughters Romena Begum, 14, and Anika, 7.
Another granddaughter Mousumi was admitted to Rangpur Medical College Hospital.
They were all resident of the India-bordering Biadanga village, Bhurangamari police Officer-in-Charge Mahfuzur Rahman said. He could not elaborate further.
The official could neither specify a reason behind the murder nor name any suspects for the killing. The locals were also unable to provide any information to the police.
Officials suspect that miscreants came from across the border late in the night and killed the victims as revenge for a murder Sultan Mia committed in India.