Since January, however, the rapid conquest and occupation of a huge area of the Democratic Republic of Congo by Rwanda and the M23 rebel group it supports has raised concerns that the principle may now be endangered.

Rwanda-backed M23 insurgents shot dead three boys who had picked up guns left by Congolese soldiers fleeing the rebel advance in eastern Congo, the U.N. said on Tuesday, adding the incident to a list of grave human rights violations reported during the conflict.

Gunfire disrupted a rally by M23 leader Corneille Nangaa in Bukavu, escalating fears of regional conflict between the Democratic Republic of Congo and its neighbors. M23 claims territorial control and is attempting to establish order,

Residents say Rwanda-backed rebels appear to be heading toward a third major city in eastern Congo. International pressure rose Tuesday over the M23’s expansion in the mineral-rich region that’s critical for global technology.