Democratic Republic of Congo's armed forces on Thursday said M23 rebels and their allies killed 50 civilians in a massacre in the eastern town of Kishishe this week, which the M23 denied.
Congo's army and the M23, a Tutsi-led militia, have been locked in fighting for months in the country's restive east, with each accusing the other of initiating attacks.
"The M23 Movement rejects the baseless allegations made against it in Kishishe," the group's political spokesperson, Lawrence Kanyuka, said in a statement. "The M23 reminds the international and national community that it has never targeted civilian populations."
The United Nations and a U.S. diplomat said they also had information about civilian killings on Tuesday in Kishishe, North Kivu province, but did not give details. Both called for an investigation.
"We are deeply saddened by the massacre of civilians in Kishishe, which could constitute a war crime," Stephanie Miley, charge d'affaires for the U.S. embassy in Kinshasa, said on Twitter.
Reports of abuse
A spokesperson for U.N. Secretary-General Antonio Guterres said the United Nations had received reports of human rights abuses committed during clashes between the M23 and local militias in Kishishe, which included a high number of civilian casualties.
Congo and U.N. experts say neighboring Rwanda supports the M23, which Rwanda has consistently denied. The two countries took part in talks last week in Angola aimed at finding solutions to the conflict.
One of their agreements was that an East African Community (EAC) regional force would intervene against the M23 if it did not stop fighting and withdraw from its positions.
Thousands protest
The EAC started sending troops into eastern Congo earlier this year to help fight various armed groups. A South Sudan army spokesman on Thursday said a battalion of 700 South Sudan troops would be sent to join the regional force.
Earlier on Thursday, thousands of people took to the streets of Goma and Bukavu, the two main cities in Congo's east, to protest the deterioration of the security situation.