Rwanda's army played a "critical" role alongside the M23 rebel group in an offensive in eastern Democratic Republic of Congo early this year that culminated in the capture of two key cities, UN experts say.

"RDF (Rwandan armed forces) operations were critical to the conquest and occupation of new territories and towns," the experts said in a report due to be published in the coming days and of which AFP has obtained a copy.

The analysis came after the DRC and Rwanda signed a peace deal on Friday in Washington to end the conflict in eastern DR Congo, where M23 fighters seized the provincial capitals of Goma and Bukavu in a lightning offensive in January and February.

Both countries pledged to pull back support for guerrilla fighters.

UN experts claim to have evidence of Rwanda involvement

Mineral-rich eastern DRC has been devastated by conflict for more than three decades, with the violence escalating in recent months as the M23 has seized large swathes of territory.

The United Nations' group of experts on the DRC said it had obtained photos, videos, drone footage, testimony and intelligence "confirming systematic and massive border incursions by RDF" and the Rwandan army's "reinforced presence" in the region.

The evidence also shows "RDF positioning at front lines and direct engagement in combat, and RDF handling of high-tech weaponry," the report said.

It said that a week prior to the attack on Goma, "Rwandan officials confidentially informed the (UN expert group) that (Rwandan) President Paul Kagame had decided to imminently take control of Goma and Bukavu."

Deadly conflict

Rwanda has repeatedly denied accusations of supporting M23 rebel group in eastern DRC.

The latest surge of violence in eastern DRC has killed thousands of people, according to the UN and the Congolese government, and deepened a humanitarian crisis facing hundreds of thousands of people forced from their homes.