Leaders from eastern and southern Africa have called for an immediate and unconditional ceasefire in eastern Congo, where Rwanda-backed rebels are threatening to overthrow the Congolese government.

Rwandan-backed M23 rebels have seized control of a mining town in eastern Democratic Republic of Congo's South Kivu province, eight sources said on Wednesday, in an apparent violation of a unilateral ceasefire they declared this week.

The government has previously refused to negotiate. But with rebels seizing another major town, a deal is the only way to prevent more deaths.