Both security forces and Kamwina Nsapu militiamen are accused of murder, mutilation, rape, and destruction of property. The death toll is in the hundreds, 1 million people have been displaced, thousands of children have been drafted in to fight. More than 40 mass graves have so far been found.
On 29 May this year, the European Union agreed sanctions against nine DRC leaders. Only one army officer was singled out: General Eric Ruhorimbere. The head of operations, who is based in Mbuji Mayi, the capital of Kasai-Oriental province, is accused of using excessive force in putting down the rebellion, which included summary executions by his troops.
The former Banyamulenge rebel fought to help topple former dictator Mobutu, then - with the support of Rwanda and Uganda, against Laurent-Désiré Kabila who had taken over the reins of power.
Ruhorimbere is suspected of being one of the Banyamulenge (Rwandophone) commanders who took part in the killing of 36 Congolese officers at Kavumu airport in South Kivu (eastern DRC) on 4 August 1998, and in further massacres in the same region in 1998 and 1999.
Ruhorimbere joined the CNDP rebel group led by Laurent Nkunda in 2007. CNDP fighters have been accused by the UN of being responsible on 4 and 5 November 2008 for the killing of some 150 people, mostly adult men, they were accusing of being anti-rebel militiamen. The atrocity was committed in Kiwanja in North Kivu.
Promoted to the rank of general in 2014, he is one of the former rebel fighters sent by President Joseph Kabila (the son of Laurent-Désiré) to a posting in the west of the country. The aim was to cut off the Rwandophone officers from their backers Rwanda and Uganda.
Other officers shifted to Kasai include General Obed Rwibasira and Colonel Innocent Zimurinda.
Violence concentrated in Kasai-Central. Kamwina Nsapu and his followers attacked the town of Tshimbulu in August 2016, then repeatedly from January this year. But government security forces pushed them back every time inflicting massive losses. Of the 42 mass graves documented by the UN, 19 are in or near Tshimbulu.
The officer in charge of operations since January 2017 is Colonel François Muhire Sebasonza . The DRC's military courts identified him as one of the 14 officers responsible for the killing of at least 200 civilians at Kitchanga, North Kivu, in February 2013. UN experts also accuse him for his alleged role in the massacre. He has not been prosecuted.
It seems Kamwina Nsapu viewed the arrival in Tshimbulu of the Rwandophone officers early this year as a foreign invasion.
However a Kasai born and bred officer, Lieutenant Julle Bukamumbe, has also been accused of a number of killings in the area.
Since the UN called for an international investigation into the Kasai killings, a number of army officers have been sent to other areas. The DRC government says it will carry out an investigation with the UN in a supporting role.