The ICRC said "very young children" were among the dead in North Kivu province following the shelling of one of only two hospitals in Kitchanga by unknown militants.
Franz Rauchenstein, head of the ICRC delegation in the Democratic Republic of Congo, said the eastern city was essentially destroyed.
"We are extremely concerned about the scale of the recent violence, which has taken place in a region already severely beset by conflicts," he said in a statement. "The presence of uncontrolled fighters in the city is also a matter of concern."
The ICRC said it's been reminding all parties to the conflict that targeting civilians is a violation of international humanitarian law.
Rebels with the March 23 Movement seized control over parts of eastern DRC last year. Reports from U.N. officials this week suggested there was renewed fighting in eastern DRC.
DRC signed a regional peace agreement recently with other African nations in a deal heralded as an opportunity to put the country on the road to peace.