South Africa often uses its diplomatic heft to position itself as defender of the "global south" on the world stage, but the deaths of 13 of its soldiers in eastern Congo fighting have exposed an inability to project hard power in its own backyard.

Residents of the besieged city of Goma, in the east of the Democratic Republic of Congo, say they are gripped by fear as gunshots continue to ring out around their homes, days after rebel forces claimed they had taken over.

U.S. Secretary of State Marco Rubio called for a urgent cease-fire in the conflict in eastern Democratic Republic of Congo saying Washington was "deeply troubled" by a recent escalation in the fighting.

Rwanda-backed rebels claimed on Monday they captured eastern Congo’s strategic city of Goma, the hub of a region containing trillions of dollars in mineral wealth that remains largely untapped.

In 2012, when M23 rebels appeared poised to seize control of a major city in eastern Congo, western countries suspended aid to put pressure on Rwanda to withdraw its support.

President Paul Kagame said Rwanda was ready for "confrontation" as he rejected criticism over his backing for M23 rebels who were pushing south on Thursday in eastern Democratic Republic of Congo after capturing the major city of Goma.

Rwanda-backed rebels claimed they captured eastern Congo’s strategic city of Goma, the hub of a region containing trillions of dollars in mineral wealth that remains largely untapped, the Associated Press reported.

The Rwandan-backed M23 rebels have released captured Romanian mercenaries who were fighting with the Congolese army. As they passed a border, they were chastised by Willy Ngoma, who tapped them mockingly one by one.

South Africa is mourning the loss of 13 soldiers who perished in the ongoing conflict in the eastern Democratic Republic of the Congo (DRC). T

Strewn with rubble from mortar and artillery fire, the eastern DR Congo city of Goma awoke on Thursday to a new abnormal -- hiding from bandits and counting the dead.

The Rwandan-backed M23 group is advancing further south in DR Congo, local and humanitarian sources told AFP Thursday, after the group vowed it would march to the capital Kinshasa.