Cross FIRs have been registered in the matter by both the groups.
Sixteen people have been arrested in connection with the violence over a land dispute that claimed six lives in a village in Deoria, police said on Tuesday. Five of the victims were from the same family.
Cross FIRs have been registered in the matter by both the groups at the Rudrapur police station here, they added.
Former district panchayat member Prem Yadav (50) was attacked with sharp-edged weapons and killed by his rival Satyaprakash Dubey and his family when he went to his house, according to police.
In retaliation soon after, Yadav's supporters from Abhaipur brutally killed Dubey and four of his family, including children, the police said.
Besides Dubey, his wife Kiran Dubey (52), daughters Saloni (18) and Nandani (10), and son Gandhi (15) were killed in the attack.
Dubey's 8-year-old son Anmol was injured and has been referred to BRD Medical College, Gorakhpur, where his condition is stated to be critical. Chief Minister Yogi Adityanath met him in the hospital earlier in the day and inquired about his well being.
The first FIR was registered by Dubey's elder daughter Shobhita Dwivedi under relevant sections of the Indian Penal Code, including 302 (murder), 307 (attempt to murder), against 77 people, including 27 named and 50 unnamed.
In another FIR lodged by rival Yadav's relative Anirudh Yadav, five victims including Dubey, his wife and children were named. The FIR was lodged under IPC sections 302 (murder), 147 (rioting), 148 (rioting with armed weapons), 149 (unlawful assembly), 34 (acts done by several persons in furtherance of common intention), police said.
Rudrapur Sub Divisional Magistrate (SDM) Yogesh Kumar said a tip-off has been received that the Yadav had built his house on government land. If the information is found true, is house would be demolished.
Deoria District Magistrate Akhand Pratap Singh said the cause behind the incident is a long-standing land dispute between the two families of the village.
"Satya Prakash Dubey's brother Sadhu Dubey had sold his land to Premchand Yadav and the matter was resolved seven years ago," the DM added.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)