The United Nations Security Council, Secretary-General Antonio Guterres and senior U.N. officials are calling for the M23 to immediately cease hostilities and withdraw from occupied territories. They have called for the withdrawal of Rwandan forces and a return to the Luanda process of mediation overseen by Angolan President Joao Lourenco.

"Active zones of combat have spread to all quarters of the city, all the neighborhoods of the city," Lemarquis, the deputy U.N. envoy and top U.N. aid official in the DRC, told reporters in New York via video from Kinshasa.

There are growing international calls for peace talks to end the escalation of violence in the east of the Democratic Republic of Congo. The fate of the economic and trading hub Goma is still unclear. UN officials have said the situation is chaotic with fighting continuing in parts of the city.

The U.N. says Rwanda-backed rebels are expanding their presence in eastern Congo after capturing the region's major city.

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.

Members of the M23 rebel group gather to supervise Congolese potential recruits for the M23 rebel group before being taken to training centres run by M23 rebels, amid clashes between M23 rebels and the Armed Forces of the Democratic Republic of the Congo (FARDC),