GENEVA — More than 40 senior military officers and officials in South Sudan should be prosecuted on charges of war crimes and crimes against humanity, a United Nations commission said on Friday, citing harrowing witness testimony and thousands of documents tying them to mass atrocities in the country’s four-year civil war.

Government and opposition forces had systematically butchered men, women and children, slitting throats, gouging out eyes, castrating and mutilating men and gang raping men and women on a massive scale, the commission said in a report it intends to submit next week to the Human Rights Council in Geneva.

“Holding those in charge in South Sudan accountable for the intentional suffering they inflict on their own people is crucial to stemming this humanitarian catastrophe,” said Andrew Clapham, a member of the commission and an international law expert.

South Sudan gained independence from Sudan in 2011, two years later plunged into a brutal ethnic conflict between President Salva Kiir’s ethnic Dinka community and the Nuer community of his former vice president, Riek Machar, creating a humanitarian disaster and what the commission described as the world’s fastest growing refugee crisis.