President Jacob Zuma has added his voice to that of other African leaders, expressing "great concern" over renewed violence this past weekend in South Sudan.

There were reports over the weekend, which marked the fifth anniversary of independence for Africa's youngest nation state, that more than 100 people were killed in gunfire.

Concerns have been raised that less than a year after the signing of an African Union-led peace agreement the country could be descending back into civil war.

In a statement issued by the department of international relations overnight, Zuma said, "these shooting incidences threaten to draw back the promising gains made through the compromised peace agreement and the recently formed transitional government of national unity".

He called on the country's two leaders, President Salva Kirr and First Vice President Riek Machar, "to provide the required leadership under these difficult circumstances".

"The President, on behalf of the government and the people of South Africa, extended his condolences to the families of those who lost their lives and wished the injured a speedy recovery."

Zuma called on the people of South Sudan "to remain calm" and he committed the South African government to providing continued support to the transitional government to ensure sustainable peace, stability and development.

Kenyan President Uhuru Kenyatta on Sunday also expressed concern over the escalating violence, while the United Nations Security Council convened an emergency meeting on the matter.

The conflict in South Sudan is expected to top the agenda at the African Union Summit, which started this week in Kigali, Rwanda, and its Peace and Security Council, which is meeting on Friday.

Former president Thabo Mbeki was instrumental in the negotiations that led to the creation of South Sudan, and Deputy President Cyril Ramaphosa has subsequently been involved in efforts to calm the infighting in the governing Sudan People’s Liberation Movement, which is the source of the conflict.