A Rwandan peacekeeper has shot dead four of his colleagues and wounded eight others in Central African Republic, the United Nations said.
The mission said the Rwandan had also died. The UN said it is opening an investigation into the incident that it called "the first of this magnitude since the establishment of the mission in April 2014".
It said the injured peacekeepers are being treated at a UN hospital in Bangui, the capital.
The UN mission statement expressed condolences to Rwanda's government and the bereaved families.
Central African Republic has been rocked by violence since the Seleka rebel coalition toppled the president in 2013.
The UN peacekeeping mission was created in April 2014 and took over the African Union peacekeeping operation there last September.