By Jenny Clover and Pete Jones
KIGALI/GOMA, Democratic Republic of Congo (Reuters) - Rwanda accused Congo on Thursday of shelling its territory and said it would not tolerate such "provocation", raising fears that violence in eastern Congo could erupt into a regional conflict.
The Democratic Republic of Congo said Rwanda's accusation was a sign Kigali wanted to intervene openly in its eastern war. Rwanda has denied accusations by U.N. experts that it covertly backs Congo's M23 rebels.
The mounting cross-border tensions came as a newly-deployed U.N. Intervention Brigade, with an unprecedented mandate to crush rebel groups, entered combat alongside the Congolese army for the first time. U.N. officials accused the M23 of firing a shell into Rwanda on Thursday which killed a civilian.
Congo and Rwanda have fought two wars over the last two decades in Congo's mineral-rich, lawless east. Rwanda has come under intense international pressure to play a constructive role for peace in its larger neighbor after rebels seized control of Goma, the largest city in eastern Congo, in November.
Regional mediators said they were "gravely concerned" by the escalation in violence and called for a return to peace talks. M23 rebels said they were ready for a bilateral ceasefire but this was promptly rejected by Kinshasa.
Rwanda said a woman was killed and a baby seriously injured by a shell that fell in its territory on Thursday.
"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," Foreign Minister Louise Mushikiwabo said in a statement.
Mushikiwabo did not say what action might be taken. She said a total of 34 rounds had been fired into Rwanda in the last month by Congolese forces: "We have remained restrained for as long as we can but this provocation can no longer be tolerated."
Kinshasa said the statement was part of a plan to justify Rwandan intervention in Congo's eastern Kivu provinces, a decade after Kigali officially withdrew troops from a previous war.
"All (Rwanda) wants to do is find a way to create permanent disorder to allow them to enter and loot the Kivus, as they have done over the last 15 years," Congolese Information Minister Lambert Mende told Reuters.
Ray Virgilio Torres, the top civilian official in the U.N. peacekeeping mission in North Kivu province, said U.N. troops had confirmed that the shell that killed the woman in Rwanda was fired by rebels in the frontline town of Kibati.
"It is something we condemn in the strongest terms, they are war crimes and something that for us remains unacceptable."
A rebel spokesman was not immediately available for comment.
Goma, the capital of North Kivu, has been at the heart of two decades of conflict stretching back to the Rwandan genocide. Since then, Kigali has repeatedly intervened in Congo, saying it had to hunt down Hutu militia who fled into Congo's lawless east after taking part in the 1994 mass killings.
The M23 is the latest incarnation of eastern Congo's Tutsi-led rebellions exploiting Kinshasa's weak grip on its borderlands, where there is a complex web of local politics and regional conflicts over ethnicity, land and minerals.
Reuters reporters in Goma heard blasts of heavy weapons from the frontline around Kibati, 11 km (7 miles) to the north. A U.N. military spokesman confirmed U.N. attack helicopters had carried out air strikes but gave no further details.
A brief rebel seizure of Goma last November embarrassed the U.N. and prompted the creation of the 3,000-strong brigade with a mandate to neutralize armed groups, including the M23.
A Tanzanian peacekeeper was killed in Wednesday's fighting, the first death since the brigade engaged rebels last week after accusing the insurgents of shelling the lakeside town of a million people.
A diplomat in the Great Lakes region said Rwanda had provided support to rebels to counter the subsequent U.N. aerial and ground assault. Rwanda blocked U.N. sanctions against two M23 leaders on Wednesday.
Regional countries, acting under an umbrella organization called ICGLR, called on Thursday for a resumption of stalled peace talks. The U.N. Special Envoy to the Great Lakes region Mary Robinson has also said for a political solution.
Global intelligence firm Stratfor said the involvement of the U.N. brigade had made a negotiated solution less likely.
"(Congo's) president will continue to push for a military solution to the crisis in North Kivu and appeal for additional support from the U.N. forces in the country," Stratfor added.
(Additional reporting by Richard Lough in Nairobi and Elias Biryabarema in Kampala; Writing by David Lewis in Dakar and Edmund Blair in Nairobi; Editing by Daniel Flynn and Andrew Roche)