* Two of the wounded are South African
* U.N. backing government offensive against M23 rebels
* Fighting raises tension between Congo and Rwanda
A U.N. peacekeeper was killed and three others were wounded on Wednesday in an operation with the Congolese army to drive back M23 rebels from the city of Goma in eastern Congo, a U.N spokesman said.
Democratic Republic of Congo's U.N. peacekeeping mission used helicopters, artillery and ground troops in support of government forces that launched the assault on rebel positions north of Goma, a city of 1 million people on the Rwandan border.
A 3,000-strong U.N. intervention brigade, with a tough new mandate to protect civilians and neutralise armed groups in the mineral-rich central African nation, sprang into action last week after the United Nations accused the rebels of shelling the city.
The M23 rebels, aware that their presence within striking distance of Goma is key to their leverage in stalled peace talks, have fiercely resisted Congolese army efforts to push them back.
Wednesday's fighting focused on the high ground around the village of Kibati, 11 km (7 miles) north of Goma.
"The M23 has been using these positions to shell populated areas. The objective of the operation is therefore to remove the threat against Goma," U.N. spokesman Farhan Haq said.
Haq did not give the nationalities of the dead and wounded. A U.N. official in Goma said Indian peacekeepers and members of the intervention brigade - composed of Tanzanian, South African and Malawian troops - had taken part in the fighting.
South African military spokesman Brigadier General Xolani Mabanga said two of the wounded soldiers were South African.
A third South African soldier was wounded in an attack over the weekend that also left two Tanzanians injured, he said.
A Congolese officer at the frontline said government troops had by early evening seized strategic hills in Kibati and were fending off attempts to retake them.
Mortar bombs and rockets have struck both sides of Congo's border with Rwanda in the past week, raising tensions between two neighbours which have fought two wars since the 1990s.
Kigali has accused Congo's army of firing on its territory, and Rwandan army spokesman Brigadier Geneneral Joseph Nzabamwita said mortar bombs had rained down on Rwanda "the whole day".
At least seven civilians were killed by shells that landed in Goma on Thursday and Saturday, humanitarian agencies and witnesses said.
Congo has blamed M23 for firing into Rwanda to try to draw in Kigali, which U.N. investigators accused of supporting the 18-month rebellion - a charge Rwanda has denied.
M23 humiliated Congo's army and the 17,000-strong U.N. peacekeeping force (MONUSCO) by briefly occupying Goma in November, forcing the government to accept peace talks.
The new U.N. intervention brigade was created in March, marking an aggressive step-up for peacekeeping operations in the region, which for years have been criticised for inaction.
Bolstered by the new brigade, Congo's President Joseph Kabila has effectively ditched the peace talks in the Ugandan capital Kampala, analysts say.
But MONUSCO chief Martin Kobler said protecting eastern Congo's largest city was the government's responsibility.
"The U.N. cannot guarantee the security of Goma. It's our partners the (Congolese army) who will do that," he said.