Goma, DR Congo / North Kivu: The United Nations said Thursday it had “consistent and credible reports” of Rwandan troops entering the Democratic Republic of Congo to back rebels battling government forces and UN troops.

Rwanda has repeatedly denied charges that it backs the M23 rebels, who occupied the city of Goma in eastern DR Congo for 10 days last November.

But as fresh fighting flared in the resource-rich region, assistant UN secretary general Edmond Mulet told the Security Council that Rwandan soldiers had assisted the fighters, according to diplomats.

On Thursday, government forces backed by UN troops shelled rebels near Goma.

Artillery fire could be heard around Kibati north of Goma, the capital of the turbulent North Kivu province, where the DR Congo army and a newly-formed UN intervention brigade have been battling M23 rebels for a week.

The UN brigade has been given the first ever mandate by the UN Security Council to launch offensive peacekeeping operations against armed groups.

As tensions ran high along the border, a Rwandan woman was killed and her baby injured in what Kigali alleged was “deliberate” cross-border shelling by the DR Congo army, the FARDC.

Mulet, however, said UN forces had witnessed M23 rebels firing artillery from into neighbouring Rwanda, according to the diplomats.

“Monusco [United Nations Organisation Stabilisation Mission in the Democratic Republic of the Congo] has not witnessed any shelling by the FARDC into Rwanda. These are areas where FARDC are not present,” Mulet was quoted as saying.

UN leader Ban Ki-moon had telephoned Rwanda’s President Paul Kagame to urge “restraint” over the mounting tensions in eastern DR Congo, Mulet told the closed Security Council meeting, according to diplomats.

His briefing is set to ignite new controversy over external backing for the rebels who have been battling the DR Congo government around the key eastern city of Goma for the past 18 months.

A UN soldier from Tanzania was killed in the fighting on Wednesday, and three South African soldiers have been hurt in the clashes.

The M23 rebels have emerged as one of the most formidable forces operating in the DR Congo’s east. They accuse the Kinshasa government of reneging on a 2009 peace pact and a deal to hold direct talks, and have threatened to attack Goma again.

Rwanda - a temporary Security Council member - has blocked a bid to impose UN sanctions on two M23 leaders as well as a council press statement condemning the death of the Tanzanian peacekeeper, diplomats said.

Rwandan Foreign Minister Louise Mushikiwabo issued a furious statement condemning the DR Congo army, accused of firing on Rwanda and supporting Hutu rebels involved in the Rwandan genocide of 1994.

“We have remained restrained for as long as we can but this provocation can no longer be tolerated. We have the capacity to determine who fired at us and will not hesitate to defend our territory. Rwanda has a responsibility to protect its population,” she said.

Western military sources who asked not to be named said that the latest clashes could be a prelude to a full-on assault by the army and UN troops. They have an unprecedented mandate to take the offensive against the armed movements long active in the mineral-rich but impoverished Kivu region.

The two eastern Kivu provinces, North and South, have been chronically unstable since two wars wracked the vast country between 1996 and 2003, drawing in armies from neighbouring and southern African countries, who fought in part over access to vast mineral wealth.

All flights to Goma, a city of a million people, have been suspended since the outlying airport is vulnerable, said a source in Monusco, the UN mission in the country.

The UN intervention force is using attack helicopters and mortars in the Kibati hills, while firing on other rebel positions with heavy artillery, according to Monusco spokesman Madnodje Mounoubai.

UN-deployed South African snipers have also reported killing six M23 rebels.

Four shells fell early Wednesday night on Goma, two of them striking the area where the airport lies east of the city, but nobody could say who fired them. Residents said shellfire killed one person and wounded about 15 others in the north of the city.