UN peacekeeping forces are engaged in heavy fighting against rebels in eastern Democratic Republic of Congo.
The head of the UN mission, Alan Doss, told the BBC that helicopter gunships and armoured units were supporting the Congolese army north of Goma.
The clashes followed reports that hundreds of protesters had attacked the mission's headquarters, saying the UN was not doing enough to protect them.
At least 20,000 people are reported to be fleeing towards Goma.
The UN is trying to help government forces prevent rebel troops loyal to renegade general Laurent Nkunda from advancing on Goma, capital of North Kivu province.
Earlier, the UN said it was considering using helicopter gunships against the rebels, but government troops were also in the area and could be hit.
Gen Nkunda has threatened to take control of Goma. His forces attacked Goma last December, but were repulsed when the UN used helicopters under its mandate to protect civilians.
A peace deal was signed in Goma between the government and various rebel groups at the end of January.