South Sudanese forces and allied militia hunted down and killed civilians, raped women and torched villages in opposition strongholds last year after a peace deal was endorsed by its president, human rights group Amnesty International said.
The government meted out "shocking" violence on individuals and entire villages in northern Leer County in the three months following a peace agreement signed in August between President Salva Kiir and his political rival Riek Machar, according to the report.
Leer is Machar's home county.
"These war crimes and other abuses committed across the country are the result of ongoing impunity that continues to fuel conflict in South Sudan, as seen in recent weeks of renewed fighting," said Amnesty senior crisis advisor Lama Fakih.
Many of the 71 people interviewed identified men and women shot dead as they fled their attackers and others executed at point-blank range, according to Amnesty.
"They shot [and killed] my brother in the river. And they shot [and killed] my stepmom in her home," Maluth, a father of three, told Amnesty about one of the attacks. "Then they caught my sister and my wife and they took them to the river and raped them."
The interviewees also described how children and elderly people were burnt alive in their homes and how girls and women were raped multiple times by multiple soldiers.
Africa's youngest nation has been in conflict since a power struggle between Kiir and Machar escalated into a military conflict in December 2013, killing tens of thousands and displacing more than 2 million people.