Andrea Drury, a representative of the International Committee of the Red Cross stationed in southeastern Katanga province, said many people in the region are living in fear because of a resumption of conflict.
"The security situation is very volatile for the moment," she said in a statement Thursday.
The U.N. Office for the Coordination of Humanitarian Affairs reported more than 400,000 people have been displaced by recent fighting in southeastern Katanga province.
Martin Kobler, United Nations envoy to the DRC, and others had expressed optimism for the republic after the rebel March 23 Movement agreed to end its campaign against the government, but international aid groups say there are dozens of other armed groups fighting in the eastern provinces.
Rwanda and DRC delegates to the United Nations exchanged barbs over the M23 during a debate Thursday at the U.N. Security Council.
Rwandan Ambassador Eugene-Richard Gasana said a U.N. report used "flawed methodology" when it suggested his country was supporting M23 rebels.
DRC envoy Ignace Gata Mavita wa Lufuta said the allegations described by a U.N. panel amounted to "serious violations" of Security Council resolutions.