South Sudan gained independence in July 2011 according to the terms of a peace agreement reached with Sudan in 2005. The agreement ended one of the bloodiest civil wars in modern history, though oil disputes, ethnic divisions and border conflicts have since threatened the deal.
Amnesty International, in 36-page report that focuses on 2011 fighting in the western part of Unity state, said foreign weapons are part of the conflict.
The organization said it discovered Chinese-made land mines placed on roads in the state. Mortar shells "likely" made by Sudanese weapons manufactures were used against civilian targets and some of the first battle tanks used by the Sudan People's Liberation Army, South Sudan's military, may have come from Ukraine.
"As the north-south conflict escalates, and with some militia groups still unreconciled with the South Sudanese government at the time of writing, the potential for further violence remains high," the report adds.
The U.N. Mission in South Sudan and the Office of the High Commissioner for Human Rights this week said likely crimes against humanity were committed during ethnic fighting in parts of the country in 2011 and 2012.