Heavy fighting was reported on Wednesday as government forces traded heavy weapons fire with the renegade militia as they geared up for an assault on Goma.
Clashes were reported in Kibumba, about 30km north of Goma, where the UN aircraft fired on NCDP positions, temporarily stalling their advance and forcing them to retreat to higher ground.
A senior aide to Nkunda, a Tutsi who says he is fighting to protect ethnic Tutsis, told AFP that the CNDP would take Goma.
After three days of fighting, the city's population has swelled with panicked villagers fleeing rural areas to escape the fighting.
Government forces are blocking roads into Goma from the north, but had pulled out in disarray from a second position further north.
The Kinshasa government accuses neighbouring Rwanda of supporting Nkunda, a charge Kigali has denied.
Nkunda's troops were "backed by Rwandan tanks which are pounding our positions from border hill positions," a government official said.
Rwanda's Tutsi-led government has repeatedly denied DR Congo's accusations that it has sent troops across the border.
The United Nations Security Council failed to reach a decision on an urgent request to reinforce UN peacekeeping troops in eastern Democratic Republic Congo (DRC) early on Wednesday.
|Monuc has been accused of failing to stop the anti-government advance toward Goma [AFP]
Alain Le Roy, the head of UN peacekeeping, briefed the council on the deteriorating situation and said that his request for additional forces had "been heard clearly by all member states".
He said that Joseph Kabila, the president of DR Congo, also made a request for a "multinational force" to support Monuc.
But the 15-member council issued only a non-binding statement in which members expressed "great concern at the resurgence of violence in eastern DRC and strongly condemned the offensive operations".
Le Roy stressed that Monuc urgently needed a special forces unit as well as air support.
"We have seen statements by the CNDP that they want to take Goma," he said.
"This is very worrying and would be very dangerous for the stability of the region."
Ron Redmond, spokesman for the United Nations High Commissioner for Refugees (UNHCR), told Al Jazeera that the prospect of violence akin to the Rwandan genocide is unlikely.
"I don't think we are approaching anything on that scale, but we are increasingly concerned about this situation," he said.
"Unfortunately it is the poorest of the poor who are the real victims in this conflict. If we are not able to help them, no one will, and that is what is so heartbreaking about this situation."
Ban Ki-moon, the UN's secretary-general, said on Wednesday that he had dispatched two of his senior aides to talk to all parties to the conflict.
"First and foremost, the fighting must be stopped," Ban told said.
"And I am deeply concerned about the civilian casualties as well as increasing number of internally displaced persons."
Joe Bavier, an independent journalist in Kinshasha, told Al Jazeera: "There are at least 850,000 internally displaced people from North Kivu province, and that was before the latest wave of fighting started in August. We're talking of another 250,000 displaced since.
"If the UN is forced to withdraw from North Kivu, you're talking about nearly a million displaced Congolese, with basically no protection from what are about about a dozen armed groups in North Kivu."