Recent acts of violence in the Democratic Republic of Congo, including the killing of foreign United Nations experts, could constitute war crimes, the International Criminal Court’s prosecutor said on Friday.

About 400 people have been killed in the Kasai region, including two U.N. experts from Sweden and the United States and their interpreter.

“There have been reports of violent clashes between local militia and Congolese forces, a large number of killings of both civilians and non-civilians, kidnappings and summary executions,” Fatou Bensouda wrote in a statement. “Such acts could constitute crimes within the jurisdiction of the International Criminal Court.”