South Sudan’s First Vice-President Riek Machar has been charged with murder, treason and crimes against humanity in a move that some fear could reignite the country’s civil war.

Justice Minister Joseph Geng Akech said the charges against Machar relate to an attack in March by a militia allegedly linked to the vice-president. The roads leading to his house in the capital, Juba, have been blocked by tanks and soldiers.

Forces loyal to Machar fought a five-year civil war against those backing President Salva Kiir until a 2018 peace deal ending the fighting in the world’s newest country, reports the BBC. Machar has been under house arrest since March, with the UN, African Union and neighbouring countries all calling for calm.

The 2018 peace deal ended the conflict that had killed nearly 400,000 people, however the relationship between Machar and Kiir has become increasingly strained amid ethnic tensions and sporadic violence.

The March attack was carried out by the White Ant militia, largely made up of fighters from the Nuer ethnic group, the same as Machar. They overran an army base in the north-eastern town of Nasir, reportedly killing 250 soldiers and a general. A UN helicopter also came under fire, leading to the death of its pilot.