South Sudan’s main opposition party says a peace agreement that ended a five-year civil war has collapsed, following the arrest of its leader Riek Machar a day earlier.

NAIROBI (Reuters) - Kenya is sending former Prime Minister Raila Odinga to South Sudan as a special envoy to help defuse a growing rift between President Salva Kiir and his longtime rival First Vice President Riek Machar which threatens to drag the country back to war.

South Sudan's First Vice President Riek Machar is under arrest and will be investigated, the country's information minister said on Friday, raising the risk that the rift between Machar and President Salva Kiir could plunge the nation back into war.

Amid rising tensions in Africa’s youngest country and reports that the country’s first vice president was arrested, Bishop Christian Carlassare called for peace.

Tensions between South Sudan's rivals threaten a fragile peace deal that ended a five-year civil war. The shooting during an evacuation mission may constitute a war crime, a UN official says.

The detention of South Sudan's First Vice President Riek Machar has effectively collapsed the peace deal that ended the 2013-2018 civil war, his party said on Thursday.

The United Nations warned that the detention of Vice President Riek Machar threatens to push the world’s youngest country back into civil war.

The papers said that Machar was removed from the vice presidency and under arrest. Machar purportedly rejected the documents and refused a request to officially resign. Machar was then relieved of his personal devices and placed under house arrest before being moved to another building within the same compound.

The reported house arrest of Riek Machar, the former bush rebel leader who became South Sudan's First Vice President, marks the latest turn in the turbulent relationship with his rival, President Salva Kiir,

United Nations secretary general António Guterres recognised Kenya's efforts to broker peace in South Sudan. A crisis has been looming in the country.