Amnesty International has accused other countries of fuelling the conflict in South Sudan by supplying weapons to the South Sudanese Armed Forces (SPLA) and opposition groups.
Sudan, China and the Ukraine were the countries accused of allegedly supplying military weapons to both sides in the conflict, the human rights watchdog said in a report.
The document, Overshadowed Conflict, Arms Supplies Fuel Violations Forgotten Conflict, focuses on the impact the flow of arms has on the civilian population.
The SPLA and the South Sudan Liberation Army (SSLA) are singled out in the report for repeatedly inflicting violence on residents of Mayom County, Unity state, and committing serious human rights violations.
Amnesty said indiscriminate attacks on the civilian population have resulted in injuries, deaths and people being forced to flee their homes empty-handed to escape the violence.
Many homes and villages have also been destroyed in the conflict, which has driven those who have managed to survive deeper into poverty.
Military weapons named in the report include Pristine 2010 Sudanese-manufactured ammunition, anti-vehicle mines from China and Ukrainian-supplied T-72 battle tanks. Amnesty said the SPLA was using the vehicles to indiscriminately shell civilian settlements.
The T-72 battle tanks had been "clandestinely delivered from Ukraine to South Sudan in 2009, involved transfers via Kenya and Uganda and included shipping companies from Germany and Ukraine and UK and Isle of Man-registered shell companies", the report said.
A former senior SSLA member apparently told the charity that his forces had received significant numbers of Kalashnikov-type assault rifles "new from the boxes", as well as ammunition, light and heavy machine-guns, B10 recoilless rifles and mortars.
The conflict in Mayom County underlines the need for governments to agree on an effective Arms Trade Treaty (ATT), according to Amnesty. The proposed treaty is due to be discussed in New York in July under the auspices of the United Nations.
"The ATT talks are an unprecedented opportunity to stop arms getting into the hands of human rights abusers. A strong treaty could help prevent many other communities suffering from the horrific cost of the irresponsible arms trade, in the way the people of Mayom County have," Amnesty's Africa director Erwin van der Borght said.
Amnesty has called on the foreign governments implicated in its report to stop supplying weapons to the warring factions.
"Governments must immediately stop supplying South Sudan with conventional arms, which have been used to commit violations of international humanitarian and human rights law, until adequate systems of training and accountability are in place," van der Borght added.
Amnesty's report has angered the SPLA, with Phillip Aguer, a spokesperson for the group, describing it as exhibiting "bias" and being "unrealistic".
"The SPLA has the mandate to protect the people of South Sudan. There is no way it can use arms and weapons meant to protect the population for attacking and displacing civilians. It does not happen anywhere," Aguer said.