United Nations forces and the Congolese army have attacked rebel positions with helicopter gunships, armoured personnel carriers and a large number of ground troops, ramping up the UN's engagement in the latest rebellion to hit the country's eastern region.
The fighting was some of the fiercest in the week since the newly created UN intervention brigade went on the offensive, and one Tanzanian peacekeeper was killed after the rebels aimed artillery fire at their position, the UN said in a statement.
Seven other troops were also wounded, UN spokesman Farhan Haq said.
"I am outraged by today's killing of a United Nations peacekeeper from Tanzania by the M23,'' said Martin Kobler, the special representative of the secretary-general in Congo, who heads the peacekeeping mission. "He sacrificed his life to protect civilians in Goma."
The fighting took place near Kibati village, about 15km from the provincial capital Goma, a city home to nearly 1 million people that was briefly captured by the M23 rebels late last year.
Haq said M23 had been using the positions "to shell populated areas" and that "the objective of the operation is therefore to remove the threat against Goma".
The UN's top military official in Congo said that at least one, and possibly two shells fell inside Goma late on Wednesday. Residents of the city's Mabanga Nord neighbourhood told Reuters that a 14-year-old boy was killed and others injured in one of the blasts.
Meanwhile, along DR Congo's border with Rwanda, a Rwandan woman was killed and her baby was
injured on Thursday in what an official alleged was "deliberate" cross-border shelling from the Congolese side.
A shell hit a market in the Gisenyi-Rubavu area of Rwanda, situated adjacent to Goma where DR Congo and United Nations troops are battling the M23 rebel faction.
The government has repeatedly accused M23 rebels of deliberately shelling across the international border in order to stoke tensions with Rwanda.
The UN involvement in the latest flare-up of violence is in sharp contrast to November, when the UN peacekeeping mission, known as MONUSCO, stood by as the rebels overtook Goma because their mandate was only to protect civilians.
The stepped-up 3,000-strong UN intervention brigade, created by the Security Council in March, is authorised to take the offensive against the rebels.
Even as forces hit rebel positions, UN officials continued to send mixed messages about the extent of their involvement, repeatedly saying they were merely "backing" or "supporting" the Congolese military, rather than
leading the offensive themselves.
"The main engagement is by the [Congolese] forces,'' said Siphiwe Dlamini, a spokesman for the South African military, which contributed troops to the brigade. "We are retaliating and going on the offensive."
Lt-Col Felix Basse, the military spokesman for the UN peacekeeping mission, also emphasised that UN forces were fighting alongside the Congolese army.
Bertrand Bisimwa, the chief of the M23 rebel movement, however, said that the UN's intervention brigade was on the frontline of Wednesday's fighting.
"It was the UN that was shooting directly at us, from their helicopters. It's the Tanzanian and South African [United Nations] troops that are on the frontline. It's them that we see first,'' he said, while describing the operation as "a big offensive" by the government, involving aircraft, tanks and infantry.
The M23 fighters launched their rebellion last year and peace talks with the Congolese government have repeatedly stalled.