The renegade general fighting government forces in eastern Democratic Republic of Congo says the ceasefire is broken and "abandoned".
Gen Nkunda says his forces will "actively defend" themselves
Gen Laurent Nkunda's force resumed fighting in late September, saying it was in response to government attacks.
Gen Nkunda told the BBC that UN peacekeepers in DR Congo have provided air support for government forces.
The fighting has forced thousands of refugees to flee to UNHCR camps near the eastern city of Goma.
They are adding to a total of 300,000 people displaced from the area so far this year, according to the UNHCR.
The general said the government was providing artillery support to local militia (known as the Mai Mai) and former Hutu members of the Rwandan army (the FDLR) who were attacking his forces.
Gen Nkunda said he had now ordered his forces actively to defend themselves.
He has repeatedly accused the Congolese army of working with the Mai Mai and FDLR to attack Congolese Tutsis, known as Banyamulenge, in his home province of North Kivu.
The general justifies his insurrection as being in "self-defence" of the Banyamulenge.
"We have told ourselves we will no longer stand with our arms crossed while people are dying. We must react. We are soldiers," he told Reuters news agency by telephone.
"Monuc thinks there is a ceasefire, but we've abandoned it."
In Kinshasa, the government has given the rebel general an ultimatum of 15 October to cease hostilities and integrate his forces into the army or face tough action.