It also says Kigali has supplied the M23 with heavy weapons and stepped up recruitment for the group.

BBC: Rwanda defence chief leads DR Congo rebels, UN report says

It also says Kigali has supplied the M23 with heavy weapons and stepped up recruitment for the group - allegations that President Paul Kagame's government has strongly denied.

BBC: Q&A: DR Congo conflict

They are often exploited by unscrupulous recruitment agencies whose exorbitant fees mean they start work with heavy burdens of high-interest debt, or by employers who withhold workers' passports and don't bother abiding by health and safety laws.

BBC: Qatar's delicate balancing act