Congos army used combat helicopters to bombard rebel fighters on Monday near the city of Goma in the first clashes in nearly six months, days before U.N. Secretary-General Ban Ki-moon was due to visit the troubled eastern borderlands.

Fighting began in the early morning after the Tutsi-dominated M23 rebels attacked government positions around 10 km (6 miles) north of eastern Democratic Republic of Congos largest city, a military spokesman told Reuters.

The M23 seized and briefly held Goma last November despite the presence of thousands of U.N. soldiers.

"The helicopters were deployed to support the army positions. The operation has finished now," Colonel Olivier Hamuli said, adding the army had called in reinforcements and used heavy weapons. "We must protect the town of Goma at all costs."

Government spokesman Lambert Mende accused the M23 of trying to disrupt the deployment of a 3,000-strong U.N. Intervention Brigade charged with neutralizing armed groups in the mineral-rich region.

The first Tanzanian troops have already begun deploying in the east.

"The M23 tried to cut the road between where the brigade will be based and Goma. They want to discourage the deployment of the brigade but they have no chance: the army will respond blow for blow," Mende told Reuters.

M23 spokesman Amani Kabasha said that the rebel group had initially responded to an attack by the FDLR, a Rwandan Hutu militia based in Congos volatile east. It had then come under attack from government artillery.

"We are not responding to their shelling, but what were hearing is not good, that (Congolese president Joseph) Kabila is sending reinforcements. He needs to calm down," Kabasha said.

No casualty figures from the clashes, which came after months of stalled peace negotiations, were immediately available.

Ban is due to arrive in Goma this week as part of a visit with the president of the World Bank, aiming to draw attention to the conflict in Congo, where millions have died during nearly two decades of violence.

The United Nations Stabilization Mission in the Democratic Republic of Congo (MONUSCO) voiced concern about the clashes, which it said took place in the localities of Kibati and Rusayo, some 12 km from Goma.

"The mission is actively pursuing a diplomatic and political solution to contain and end the clashes," it said in a statement.