The United Nations expressed deep concern at reports of M23 rebels and Rwandan troops advancing south towards the Congolese city of Bukavu on Thursday, as the militants sought also to assert their control over east Congo's largest city Goma.

Kagame's comments clearly suggested that he wants South Africa to back off from DR Congo, where its military involvement dates back to the late 1990s. It first joined the UN's peacekeeping mission, Monusco, following the end of the racist system of apartheid in 1994.

A Rwanda-backed militia seized the pivotal Congolese city of Goma this week, threatening a new humanitarian crisis after decades of fighting.