A United Nations Group of Experts said it has "solid evidence" that Rwandan troops have been fighting alongside the M23 rebel group in eastern Democratic Republic of Congo and providing it with weapons and support.

The findings were contained in a confidential report seen by Reuters on Thursday.

Rwanda has previously denied accusations by Congo's government that it supports the M23 and that it has sent troops into the country. The M23 has denied it receives Rwandan support.

The U.N. group "obtained solid evidence of the presence of, and military operations conducted by, RDF (Rwandan Defence Force) members in Rutshuru territory between November 2021 and July 2022," the report said.

RDF members conducted joint attacks with M23 fighters against Congo's army and Congolese armed groups, and provided the rebels with weapons, ammunition and uniforms, it said.

Yolande Makolo, Rwanda's government spokesperson, said in a statement the government wouldn't comment on an "unpublished and unvalidated report." She said an earlier report by the experts' group in June "contained none of these false allegations."

Congo's government spokesman Patrick Muyaya said he welcomed the work of the U.N. group.

"The truth always triumphs in the end. We hope that conclusions will be drawn quickly to put an end to Rwanda's interference and bring back lasting peace," he wrote on Twitter.

The M23 insurgency stems from the long fallout from the 1994 genocide in Rwanda. The group was formed in 2012 claiming to defend the interests of Congolese Tutsis, the ethnic group shared by Rwanda's President Paul Kagame, against Hutu militias.

Since May, the M23 has waged its most sustained offensive in years, killing dozens and displacing tens of thousands of people. By July, it controlled a territory almost three times as large as it did in March, the U.N. group said.

The M23's resurgence has inflamed regional tensions and spurred deadly protests against the U.N. peacekeeping mission in Congo, which civilians accuse of failing to protect them.

The U.N. group detailed evidence including photos of Rwandan soldiers in an M23 camp, drone footage showing columns of hundreds of soldiers marching near the Rwandan border, and photos and videos showing M23 fighters with new uniforms and equipment similar to those of the Rwandan army.

Rwandan troops and the M23 jointly attacked the Congolese army camp in Rumangabo in May, it said. When the M23 took control of the strategic border town of Bunagana in June, Rwandan soldiers were either present or had provided equipment to the rebels, the report said.

Rwanda and neighbouring Uganda have a long history of military intervention inside Congo. The two countries invaded in 1996, and again in 1998, claiming they were defending themselves against local militia groups.

A target of the M23 and Rwandan operations in Congo has been the Democratic Forces for the Liberation of Rwanda (FDLR), a Hutu militia which Rwanda accuses Congo of using as a proxy. Congo's government has denied this.

Some members of Congo's army have supported and fought alongside a coalition of armed groups including the FDLR, the U.N. report said.