Battles over cattle between rival factions of the Dinka people, the Rup and Pakam clans, broke out on December 6 in the central area of Western Lakes, some 250 kilometres (155 miles) northwest of the capital Juba.
"More than 60 people were killed, and dozens wounded,"Akol Paul Kordit, a local MP who also serves as the country's deputy information minister, wrote in a statement.
Fighting continued with the latest raid at dawn on Friday, it said.
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. Women are commonly raped and children abducted, adding fuel to revenge attacks.
Presidential spokesman Ateny Wek Ateny confirmed the "senseless" attacks, and said security chiefs had been summoned to a meeting on the violence.
"We condemn it in the strongest terms possible," he said.
Such attacks have worsened amidst the breakdown of society during the four-year civil war which began in December 2013.
Half the country is in need of emergency food and a third has been forced from their homes since then, according to the UN.
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