A rebel alliance claimed the capture of the biggest city in the Democratic Republic of Congo’s mineral-rich eastern region this week, pushing back against resistance from government troops backed by regional and UN intervention forces.

United Nations Secretary-General Antonio Guterres on Tuesday spoke separately with the presidents of the Democratic Republic of Congo and Rwanda about the escalating conflict in eastern Congo, U.N. spokesperson Stephane Dujarric said.

M23 rebels in the Democratic Republic of Congo were reported to have taken the key eastern city of Goma in fierce fighting with government forces that sent streams of refugees fleeing area communities.