Emotions are still running high after the killing of civilians in Kishishe, in the chiefdom of Bwito, Rutshuru territory, about 100 kilometres from Goma in the east of the Democratic Republic of Congo.
According to the Congolese army, 50 civilians were killed by the M23 rebels with the massacre being condemned by various agencies.
In the DRC, the government declared three days of national mourning while the United Nations Organisation Stabilisation Mission in the Democratic Republic of the Congo (Monusco) denounced "these appalling acts".
In its statement, Monusco called on "all relevant authorities to investigate without delay and bring the perpetrators to justice".
Amnesty International also reacted by calling on M23 to cease targeting civilians following the killing of dozens of non-combatants in towns in the east of the DRC in recent days in indiscriminate attacks and, in some cases, summary killings.
"The M23 rebel group must immediately end deliberate and indiscriminate attacks on civilians,” said Flavia Mwangovya, Amnesty International's deputy director for East Africa, the Horn and Great Lakes Region.
"We urge all forces in the area, including the Congolese army and the East African Community Regional Force, to take all necessary measures to protect the civilian population while respecting international humanitarian law," Ms Mwangovya added.
Human Rights Watch is also calling for an independent investigation and sanctions. The massacre of civilians in Kishishe could constitute a war crime, said Stephanie Miley, chargé d'affaires of the US embassy in Kinshasa.
Young men targeted
According to local civil society sources in North Kivu, the M23 targeted young men from Kashishe who had previously ambushed the rebels through community defence groups. The bloody attack also claimed the lives of children and elderly people.
According to the Congolese army (FARDC), several other civilians are now missing or have been kidnapped by the M23.
General Sylvain Ekenge, the spokesman of the Congolese army, also denounced the forced recruitment of young people by the M23 and the use of children in the fighting.
The fighting resumed Thursday in North Kivu in violation of the ceasefire decreed in Luanda, Angola.
On November 23, East African heads of state and other political leaders from the region declared a ceasefire.