The two families had clashed over throwing rubbish in 2013.
Six members of a family, including three women, were shot dead in Madhya Pradesh's Morena after a land dispute turned violent. Two other men have been hospitalised with severe injuries.
Shocking video footage of the incident showed several men carrying rifles shooting at an unarmed group of people after the latter were thrashed with wooden sticks.
The incident happened around 10 am at Lepa village, 50 to 60 km from the district headquarters, between the families of Dheer Singh Tomar and Gajendra Singh Tomar.
The two families had clashed over dumping waste in 2013. Two people from Dheer Singh Tomar's family were killed then, and Gajendra Singh Tomar's family fled the village.
The two families had reconciled outside a court, and the latter's family had returned to the village today. Dheer Singh Tomar's family allegedly launched a pre-meditated attack on them with sticks and opened fire.
Gajendra Singh Tomar and his two sons were among the six who were murdered.
Asked about the motive behind the killings, police said that the two groups had an old enmity.
"The victims' relatives have been accused of murdering the family members of today's alleged killers," an official said.
Police have identified eight people who were allegedly involved in the murders and a case is being registered against them, they said.