A group of defectors fighting for the M23 rebel movement against the Congolese army say that they were recruited and trained in neighbouring Rwanda against their will.
The revelations come after weeks of fighting in the east of the country and would be the first direct evidence that Rwandan troops are involved in the fighting that has displaced thousands from their homes.
The allegations made by the rebel defectors across the border in the Democratic Republic of Congo will strain relations with Rwanda, but so far officials from both sides have held back, and are talking about a joint investigation to get to the bottom of the matter.
Speculation of Rwandan involvement in the mineral-rich zone grew as the UN mission said this week 11 rebel fighters had given themselves up in Congo, saying they had been recruited in Rwanda and tricked into crossing the border to fight for the rebels.
Rwandan Foreign Minister Louise Mushikwabo rejected the assertions as untrue and accused the UN of stirring tensions in the Great Lakes region.
"She has requested Roger Meece to come to Kigali to explain why MONUSCO is spreading false rumours aimed at aggravating the volatile situation. .. [and] undermining ongoing collaboration between Rwanda and DRC [Congo]," a foreign ministry statement said of the head of the local UN peacekeeping mission MONUSCO.
There was no immediate reaction from MONUSCO but earlier this week one of its officials said it was clear from their contacts with the fighters that they were Rwandan, without going as far as implying direct involvement of Rwandan authorities.
"They gave us information about where they came from, where they were recruited, before being taken to the frontline ... The fact that they're Rwandan, I think that it's undisputable," Patrick Cyrille-Garba, head of the UN disarmament programme in North Kivu, told Reuters.
Cyrille-Garba said three more fighters also alleging to have been forcibly recruited in Rwanda had since given themselves up and were now being questioned by MONUSCO with the 11 others.
Rwanda has in the past backed rebels in Congo, citing a need to stamp out fighters who operate there and who are linked to its 1994 genocide.
The two neighbours have enjoyed warmer ties since 2009 when the Rwandan-backed CNDP rebel group signed a peace deal and integrated into the Congolese armed forces.
However the eastern Congolese provinces of North and South Kivu have experienced new fighting in recent weeks after former CNDP elements launched a fresh rebellion, rallying behind the renegade Congolese general, Bosco Ntaganda.