The UN on Tuesday said the humanitarian situation in the besieged DR Congo city of Goma was "extremely worrying" amid mass displacement, food shortages, looted aid, overflowing hospitals and widespread sexual violence.

Bodies are lying on the streets. Medical staff in overwhelmed hospitals are treating hundreds of wounded civilians against the backdrop of gunfire and mortar fire.

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.

Speaking to BBC Newshour while being locked down in a UN bunker in the city, the deputy head of the UN force, Vivian van de Perre, said the M23 rebels had "established" themselves in Goma, but were still facing "pockets of resistance".

"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.

Thousands fled the city of Goma on Monday as fighting raged between Congolese forces and rebels backed by neighboring Rwanda, who claimed to have captured eastern Congo’s largest regional hub.

Fighting with M23 rebels in eastern Democratic Republic of Congo left six United Nations peacekeepers dead, UN officials said Saturday.

Fighting has escalated sharply in recent weeks in eastern Congo, where rebels have seized key towns and are closing in on the city of Goma, the government’s last stronghold in the North Kivu province,

Goma's streets saw bodies recovered as M23 rebels urged normalcy. President Tshisekedi promised a strong response. M23 forces advanced toward South Kivu.

Reuters quoted the spokesperson as saying that the UN is deeply concerned by these developments, which are backed by "credible reports."