The Rwanda-backed rebels who captured a major city in eastern Congo have sought to reassure its residents about their safety.

Rwandan-backed M23 rebels in Democratic Republic of Congo are seeking to advance south towards Bukavu, the capital of South Kivu province, in an attempt to expand their area of control in the country's east after capturing the city of Goma.

Fighting last week between government forces in the Democratic Republic of the Congo and Rwanda-backed rebels in the major eastern city of Goma left at least 900 people dead, the UN health agency has said.

Bodies are decomposing on the streets of Goma that have not yet been collected, with hundreds of thousands displaced in the region after fighting between Rwanda-backed rebels and Congolese forces.

Advances being made by the M23 rebel group in the Democratic Republic of Congo are "heightening the threat of a regional war," according to U.N. Secretary General Antonio Guterres.

A rebel group that claimed to have captured the city of Goma in the eastern Democratic Republic of Congo last week has called for an immediate humanitarian ceasefire, after fighting with the Congolese military has left hundreds of people dead.

Rebels occupying the eastern Democratic Republic of Congo city of Goma have declared a cease-fire but the government dismissed the pause in the fighting as a ruse aimed to head off growing international concern.