The incident happened in Sirum Ambatoli village on Saturday, the police said.
Porta Munda (45) and his sister Paru Kumari (30) were killed by unidentified miscreants on Saturday night, Sub-Divisional Police Officer (Khunti), Ranveer Singh said.
Witchcraft could be one of the reasons behind the attack and murder, he said.
On being informed about the incident, a police team rushed to the spot and recovered the bodies, he said, adding investigations were on.
In a similar incident on Saturday, a 35-year-old woman was killed by her neighbours in Baskonagar under the jurisdiction of Adityapur police station of adjoining Seraikela-Kharswan district.
The tribal woman had gone to fetch water from a nearby tubewell when one Vijay Haiburu attacked her with a lathi and Vijay's father Chand Haiburu slit her throat with a sword, police said.
The accused were arrested, the police said.
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