Dissident soldiers in the Democratic Republic of Congo have attacked army positions in the east of the country, the government says.
Mr Nkunda says the minority Tutsi community has been excluded
The attacks, close to the Rwandan border, ended months of relative calm in the region.
The army said troops loyal to dissident general Laurent Nkunda bombarded the town of Sake for several hours.
United Nations officials said thousands of civilians had fled their homes to escape the violence.
The fighting comes amid heightened tension in the Congolese capital, Kinshasa, where the former rebel leader, Jean-Pierre Bemba, is challenging his defeat in last month's presidential elections.
At least two soldiers are reported to have been killed by in the attacks, in which the dissident troops used machine-guns, mortars and rocket-propelled grenades.
Army commander Col Delphin Kahindi, speaking from Sake, said 15 people, including eight civilians, had been wounded in five hours of clashes in which his troops repulsed Mr Nkunda's fighters.
Sake is a small town about 25km (15 miles) west of the provincial capital of Goma.
Maj Ajay Dalal, a spokesman for the Indian UN peacekeepers in the area, said rebel forces appeared to be pulling back into the bush
"For now, the firing has stopped. We are deployed all around and are supporting the Congolese army but we haven't had to engage yet," he said.
Mr Nkunda left the army and launched his own low-level rebellion after Congo's war ended, saying that the country's transition to democracy was flawed and had excluded the minority Tutsi community.