JUBA - South Sudan's opposition said on Thursday the arrest overnight of First Vice President Riek Machar, long-time rival to President Salva Kiir, had invalidated their 2018 peace deal and risked plunging the country back into war.

A power-sharing deal between President Kiir and VP Machar has been gradually unraveling, threatening a return to the civil war that killed around 400,000 people between 2013 and 2018.

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.