Rebels in the Democratic Republic of Congo battling government and UN troops announced a withdrawal Friday, as neighbouring Rwanda dismissed accusations to say its soldiers are not "yet" fighting after days of escalating violence.

Rebels in the Democratic Republic of Congo battling government and UN troops announced a withdrawal Friday, as neighbouring Rwanda dismissed accusations to say its soldiers are not "yet" fighting after days of escalating violence.

Heavy battles around the resource-rich eastern city of Goma between M23 rebels and the government -- backed by a newly deployed special offensive United Nations force -- come amid fresh UN accusations Rwandan troops are actively backing the rebels.

New fighting flared this week as government and UN troops pounded rebel positions, raising fears the conflict could drag neighbouring nations back into open warfare over the key mining region.

On Thursday, the UN said it had "consistent and credible reports" of Rwandan troops entering DR Congo to support the rebels, but Rwandan Foreign Minister Louise Mushikiwabo scotched the reports, in a brief comment made on Twitter.

"Rwandan troops are not in DRC (yet), when they are, you will know," she wrote Friday, without giving further details.

Rwanda has always flatly denied supporting the M23, a predominantly ethnic-Tutsi force that deserted from the Congolese army last year to turn its guns on its comrades, briefly seizing Goma in November.

In DR Congo's capital Kinshasa, Information Minister Lambert Mende said government and UN troops had pushed forward from the flashpoint city to take back territory in the surrounding hills from the rebels.

"We achieved most of our goals," Mende told reporters, adding that the aim was to drive rebels from hilltop positions up to 15 kilometres (nine miles) north of Goma, including strongholds from where he said the M23 are taking pot shots at civilians.

Rebel leader Bertrand Bisimwa told RFI radio that fighters had "pulled back from the frontline... to allow the fighting to stop."

Tensions have risen yet higher after Rwanda accused Kinshasa's forces of also firing multiple shells and rockets across the border into its territory, killing at least one woman.

"We have remained restrained for as long as we can but this provocation can no longer be tolerated," Mushikiwabo said in a furious statement late Thursday. "We have the capacity to determine who fired at us and will not hesitate to defend our territory."

But despite holding a rotating seat at the UN Security Council, Rwanda is diplomatically "very isolated internationally," said Thierry Vircoulon of the International Crisis Group, noting that the country also has little room to manoeuvre on the ground.

"The problem now is that the peacekeepers are involved, so there is a risk of confrontation between peacekeepers and Rwanda, which would be disastrous for them," Vircoulon added.

The European Union warned against any move that could risk broadening the conflict, in a region still reeling from back-to-back wars that drew in much of the region from 1996 to 2003.

"I firmly condemn repeated M23 attacks against both (UN peacekeepers) and the civilian population, as well as any attempt to internationalise the conflict," EU foreign policy chief Catherine Ashton said.

"Any direct intervention by DRC's neighbouring countries can only exacerbate the situation," she said, adding that a high-level delegation of top envoys from the EU, African Union, United States and UN would travel to the area in the coming days.

On Wednesday a UN soldier from Tanzania was killed and three others wounded in the fighting, UN and military sources said.

An AFP reporter in Gisenyi, the Rwandan town bordering Goma, said that all was calm with shops open, and no noticeable increase in military presence.

The border remains open, with traders coming and going apparently as usual, although all flights to Goma -- a city of a million people -- are reported to have been suspended.

UN leader Ban Ki-moon said Friday he was "deeply concerned about the escalating violence", adding that "spoilers" fuelling the conflict must be held to account.

Meanwhile South Africa, whose troops are part of the UN intervention force, warned M23 on Friday not to try to retake Goma.

"We're trying to send a message to the M23, this time around you're not going to see Goma," South Africa defence chief Derrick Mgwebi said Friday. "Don't venture in ideas of taking over again."

South African snipers have killed at least six M23 fighters in recent days as helicopters hit rebel positions from the air.

The 3,000-strong special UN force has an unprecedented offensive mandate to attack rebel troops, marking a strategic change of tack from traditional UN missions.