Dut Achuek, a state minister, said eight people died in an attack on Monday in Jonglei state, while a follow-up raid on Tuesday left "23 women killed and... 19 men killed."
Most of the victims were civilians whose homes were burned and livestock stolen, Achuek said.
Both attacks, by armed men from the Murle ethnic group, targeted Dinkas living in villages around 150 kilometres north of Bor, the state capital.
Kudumoc Nyakurono, information minister for neighbouring Boma state, confirmed the involvement of Murle militia from the area.
Rival pastoralist communities in South Sudan have a long and bloody history of tit-for-tat raids in which cattle are rustled and property looted, and women are commonly raped and children abducted, adding fuel to revenge attacks.
In one of the worst such cases, over 3,000 people were killed when members of a well-armed Nuer militia attacked the Murle in 2012.
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