S. Sudan peace deal collapse risks 'all-out war': UN experts

South Sudanese President Salva Kiir (left) and Vice President Riek Machar after peace talk at the State House in Juba, on December 17, 2019. [AFP]

Failure to uphold South Sudan's peace accords could trigger a "catastrophic" return to war and threaten millions of lives, the UN commission documenting rights abuses in the country warned Thursday.

South Sudan's opposition said the arrest overnight of First Vice President Riek Machar, the long-time rival to President Salva Kiir, had invalidated their 2018 peace deal, the cornerstone of the nation's fragile stability.

The arrest, alongside mounting military clashes and reported attacks on civilian populations, "signals a severe unravelling of the peace process -- and a direct threat to millions of lives", the United Nations Commission on Human Rights in South Sudan said in a statement.

"Failure to uphold the protections enshrined in the Peace Agreement -- including freedom of movement, political participation, and the cessation of hostilities -- will lead to a catastrophic return to war."

Adhering to the agreement and protecting civilians are "critical to preventing all-out war", the experts said.

The commission said that throughout March, violence had intensified in several regions, and armed confrontations had crept closer to the capital Juba, amid reports of opposition figures detained without due process in violation of the peace deal's provisions on political inclusion and rule of law.

"The deliberate targeting of opposition leaders and civilians represents a reckless disregard for international law and the country's future," said commission chair Yasmin Sooka.

"The Peace Agreement is not optional: it is binding. Its systematic undermining by political and military actors is not only unlawful but a betrayal of the South Sudanese people who have already endured years of devastating conflict."

The commission said the situation was being exacerbated by the deployment of Ugandan troops and tanks following a request from Kiir, which they said raised serious concerns over potential violations of the UN arms embargo.

"We must not allow South Sudan to repeat the mistakes of the past," said commissioner Barney Afako.

"Failure to de-escalate the ongoing political and military tension will be cataclysmic for South Sudan. South Sudan's leaders must urgently sit down across political divides to de-escalate tensions, reassure an alarmed population, and address their differences," he said.

He said the international community should move quickly "to prevent South Sudan from imploding and aggravating the volatility of this fragile region".

The three-member commission is an independent body mandated by the UN Human Rights Council in 2016.