The armed forces say the rebel group also violated a five-day-old ceasefire in the east of the country.
The armed forces of the Democratic Republic of the Congo (DRC) have accused the M23 rebel group and its allies of killing 50 civilians in the eastern town of Kishishe.
The army said in a statement on Thursday that the massacre took place on Tuesday, as it also accused the rebels of violating a five-day-old ceasefire in the east of the country.
Tens of thousands of people have been displaced because of the resumption of fighting last month between the armed forces and the M23, which has been waging its most serious offensive in eastern DRC since 2012.
General Sylvain Ekenge told the AFP news agency that M23 was “carrying out massacres … the most recent of which is that of 50 Congolese civilians, heinously murdered on Tuesday in Kishishe,” a village some 70km (40 miles) north of the eastern city of Goma.
He claimed that the DRC forces had maintained the truce, but the rebels had attacked government positions.
M23 leader Bertrand Bisimwa told the Reuters news agency that the group would respond to the accusations later in a statement.
A mostly Congolese Tutsi group, the M23 first leaped to prominence in 2012 by briefly capturing the city of Goma. After a peace deal in 2013, many M23 fighters were integrated into the military.
The group resumed fighting in late 2021, saying the DRC had failed to honour a pledge to integrate its fighters into the army, among other grievances.
The United Nations and international rights group Human Rights Watch (HRW) said they were aware of the killings in Kishishe in North Kivu province, but could not provide details or information about the number of fatalities.
The DRC has accused its neighbour, Rwanda, of supporting M23, a charge that Kigali has denied.