In a statement, spokesman General Sylvain Ekenge said the M23 group was "carrying out massacres... the most recent of which is that of 50 Congolese civilians, heinously murdered on Tuesday in Kishishe," a village north of the eastern city of Goma.

Fighting with heavy weapons erupted between both sides earlier in the day, shaking the five-day-old truce.

The ceasefire took effect in North Kivu province at the weekend following a summit between DRC and its smaller neighbour Rwanda.

It was to have been followed by a rebel pullout from captured territory, a withdrawal that has yet to take place.

Kinshasa accuses Rwanda of providing M23 with support, something that UN experts and US officials have also pointed to in recent months.

But Kigali disputes the charge.