President Salva Kiir and his rival, Vice President Riek Machar, agreed on the creation of a unified armed forces command, one of several crucial unresolved issues holding up implementation of the 2018 deal to end the country's bloody five-year civil war (AFP)

Amnesty International on Wednesday urged the African Union to take "long awaited" steps toward creating a promised war crimes tribunal to try atrocities committed during South Sudan's bloody five-year conflict.

The establishment of an AU-led 'hybrid court' to prosecute those responsible for war-time atrocities was first agreed in a 2015 peace deal and again in 2018, but never implemented.

Government and rebel forces were accused of heinous crimes including gang rape, ethnic massacres and enlisting child soldiers during a civil war that left nearly 400,000 people dead in the world's youngest nation.

Amnesty and the South Sudanese Transitional Justice Working Group, a coalition of civil society and faith-based groups, said the AU must empower a court to investigate "the most serious crimes on the continent".

"The formation of this Court should not have been delayed for so long. The AU must take long awaited and bold action," Muleya Mwananyanda, Amnesty's director for East and Southern Africa, said in a statement.

"The failure to establish the Hybrid Court reflects a lack of political will in South Sudan's government to hold those most responsible for serious crimes, which are likely to include senior political and military officials, to account."

Two years after separating from Sudan in 2011, oil-rich South Sudan plunged into war after President Salva Kiir accused his then-deputy Riek Machar of plotting a coup.

The conflict that followed was marked by ethnic violence on a particularly brutal scale, as battles erupted between people from Machar's Nuer community and Kiir's Dinka tribe.

UN investigators warned ethnic cleansing may have occurred in South Sudan, where rape and starvation were used as weapons of war, and civilians murdered wholesale in gruesome attacks.

Kiir formed a power-sharing government with Machar in 2020 after signing a peace deal and recommitting to try the worst abuses in a special court administered with the AU.

But the government has been accused of trying to block such a tribunal, and deliberately frustrating efforts to bring those responsible for possible war crimes to justice.

James Ninrew, chair of the Transitional Justice Working Group, said that given its unwillingness to pursue perpetrators, the AU should not place the court in South Sudan but elsewhere in Africa, and must ensure its judicial independence.

The establishment of a court would "show that the AU stands with survivors and victims of crimes for which impunity cannot be tolerated", said Mwananyanda.

The AU Peace and Security Council, the bloc's foremost conflict resolution body, is scheduled to convene on South Sudan on November 30.