The Rwanda-backed rebel group M23 is battling Congolese government forces in Congo's key city of Goma, causing the international airport there to be evacuated.

Nine United Nations peacekeepers in eastern Congo sustained injuries during fighting with the M23 armed group, the U.N. said, as the rebels close in on Goma.

The calls come after 13 soldiers serving with peacekeeping forces in the DR Congo were killed in clashes with M23 rebels, UN and army officials have said. South Africa said nine of its soldiers were killed while deterring an advance on Goma.