Government and opposition forces in South Sudan's conflict may both have committed war crimes and must resolve the strife by negotiating, a U.S. activist said. "I believe war crimes appear to have been committed by both sides in this conflict, and the nature of targeting on the basis of ethnicity has made a resolution of this war much more difficult," said John Prendergast, co-founder of the Enough Project. "The level of destruction and loss of life in Bor was indeed catastrophic, and given its history even more heartbreaking for the people there, but there are other areas of the country that have suffered greatly as well," Prendergast said after visiting the Jonglei state, the Sudan Tribune reported Tuesday. . Violence broke out in Juba in mid-December and spread to three of the country's 10 states as forces loyal to President Salva Kiir fought anti-government forces linked to former Vice President Riek Machar, who Kiir dismissed. Officials say thousands of people have been killed and nearly a million have been displaced. Prendergast said it was becoming more urgent for the two sides to resolve the conflict at the negotiating table, not on the battlefield. "That requires leadership, which South Sudan requires more than ever," Prendergast said. The Enough Project was founded in 2007 to help end genocide and other crimes against humanity.