The report, seen by the BBC, says the rebels continue to receive arms supplies and recruit fighters.
It says the UN has failed to stop the illegal trade in minerals and has exacerbated the humanitarian crisis.
The report is by the Group of Experts, mandated by the UN to probe violations of the arms embargo in DR Congo.
It states that the UN-backed military operation against Rwandan-Hutu rebels has failed to dismantle the organisation's political and military structure.
Instead, these rebels - some of whose leaders were involved in the Rwandan genocide - have been able to use networks in Burundi, Uganda, Tanzania, and overseas in Europe and North America, to bolster their supply of arms and to recruit extra soldiers.
Gold and tin
The report says Rwandan fighters continue to enjoy support from senior members of the Congolese military who are supposed to be opposing them.
This militia, known as the Democratic Forces for the Liberation of Rwanda (FDLR), controls parts of the illegal trade in gold and tin, worth millions of dollars a year.
The report says that former Rwandan-backed Congolese Tutsi rebels are operating as a parallel armed group, despite integrating with the national army.
It adds that they have expanded their influence throughout the region under the command of Bosco Ntaganda, and unleashed a wave of killings, rapes and looting within the framework of the military operation.
Known as "the Terminator", Gen Ntaganda is wanted by the International Criminal Court for alleged forced enrolment of child soldiers in 2002-2003.
He formerly served in a Tutsi-dominated rebel militia, the Congress for the Defence of the People, but joined the national army at the beginning of this year.
The report found that Gen Ntaganda's men were deployed in some of the region's most lucrative mining areas, which they now control.
The UN experts have found that some companies, already named in a report last year, continue to work against UN sanctions.
The report says that significant amounts of gold are being trafficked throughout the region, particularly through Uganda and Burundi and then sold to individuals in the United Arab Emirates.
The Group of Experts recognises that there may well be a contradiction in the mandate of Monuc, the UN peacekeeping force in the DR Congo.
They say it has to both protect civilians as well as back a military operation that has aggravated the humanitarian situation in eastern Congo.
