It says civilians and militia members who had been captured by the M23 rebel group were killed in the village of Kishishe between last November and April.

Rwanda has denied backing the M23 rebels who have in the past said they were not behind the massacre.

HRW has called on the Congolese government to get help from the UN and African Union to conduct proper exhumations, return remains to families and hold those responsible to account.

Who are M23 fighters?

• Largely made up of Congolese army deserters, they first took up arms in 2009 accusing the government of marginalising the country's ethnic Tutsi minority and failing to honour previous peace accords
• Early last year they began regrouping, a decade after disarming as part of peace agreement
• They captured territory in North-Kivu province and hundreds of thousands of civilians fled their homes
• They have since pulled back from some areas as part of a regional ceasefire initiative
• But the group says it will not disarm unless the government agrees to direct talks.