* United Nations says will halt any rebel advance on Goma
* Army says situation under control, pushing back rebels
* United Nations says Uganda's ADF rebel attacked convoy
* U.N. Intervention Brigade patrolling but not in combat (Adds details)
C ongolese government forces supported by helicopters attacked M23 rebel positions near the eastern city of Goma on Tuesday in a third day of heavy fighting that has forced hundreds of villagers to flee their homes and raised tensions with Rwanda.
The clashes have focused attention on the role of the United Nations, which is deploying a new force with a mandate to attack rebel groups in eastern Democratic Republic of Congo.
The 3,000-strong Intervention Brigade, made up of South African, Tanzania and Malawian troops, has begun patrols but not yet engaged in combat.
The United Nations has warned it would block any attack on Goma, a city of one million people bordering Rwanda, which was briefly captured by rebels in November.
A Reuters reporter in Mutaho, some seven km (four miles) northeast of Goma, saw three army helicopters bombard rebel positions in the town of Kibati, four km further north.
"The situation is now calm," army spokesman Colonel Olivier Hamuli told Reuters in Mutaho. "They attacked us at 4 o'clock this morning but we replied ... Our aim is to wipe out the M23."
Rebels and government troops had traded mortar fire on Monday close to the northern and western outskirts of Goma. The United Nations said that a shell fell on Tuesday 100 metres (yards) from Goma airport, with no victims reported.
Moustapha Soumare, U.N. humanitarian coordinator in Congo, warned that a return to fighting so close to inhabited areas placed thousands of civilians at risk.
Millions of people have died from violence, disease and hunger since the 1990s as foreign-backed rebel groups have fought for control of eastern Congo's rich deposits of gold, diamonds, copper, cobalt and uranium, destabilising the Great Lakes region at the heart of Africa.
Kinshasa has claimed that Rwanda was directly backing the Tutsi-led M23 rebels. A U.N. report said the group recruits in Rwanda with the aid of sympathetic military officers.
Colonel Hamuli showed Reuters two dead M23 fighters and two prisoners who he said had come from Uganda and Rwanda. One of the prisoners said he came from the Ugandan town of Rubaya, but it was not possible to verify this.
Both Rwanda and Uganda, which have in the past backed insurgents in Congo, deny any support for M23. Kigali accused Kinshasa and U.N. troops on Monday of "provocative and deliberate" shelling of its territory, though it said no one was wounded.
ATTACK ON U.N. PATROL
The 17,000-strong U.N. force in Congo (MONUSCO), the world's largest peacekeeping mission, has been deployed for more than a decade but has failed to stem a conflict involving dozens of armed groups and complicated by national and ethnic rivalries.
The arrival of the Intervention Brigade has raised peace hopes. The World Bank is offering $1 billion to regional governments to promote development if they respect a U.N.-brokered February deal not to back rebels in Congo.
Peace talks between the Congolese government and M23 in Kampala, the capital of neighbouring Uganda, have stalled.
"We have to go back to the negotiating table in Kampala. The solution has to be a political not a military one," M23 spokesman Amani Kabasha told Reuters.
Congolese government spokesman Lambert Mende in Kinshasa said 180 rebels had been killed in the fighting but the government was still open to peace negotiations. Both sides in the conflict routinely exaggerate death tolls.
The Red Cross estimates that 66,000 Congolese have refugees fled into Uganda since Thursday after attacks by the ADF, an Islamist group which Kampala says is allied to elements of Somalia's al Shabaab movement, an al Qaeda-linked group.