Forces from the rebel March 23 movement in the Democratic Republic of Congo pulled back from Goma, the capital of North Kivu province this month. The rebel movement formed after complaining the government in Kinshasa reneged on peace agreements.
Moustapha Soumare, the U.N. humanitarian coordinator for DRC, said following a weekend visit to the region that some aspects of normal life had returned to Goma.
"Without minimal security guarantees, it is difficult for us to work," he added in a statement. "We want to avoid at all cost that the aid we deliver will not expose the beneficiaries to attacks by armed elements."
M23 rebels are suspected of committing crimes against humanity. The Rwandan government, meanwhile, has denied allegations it was backing the rebel movement.
Herve Ladsous, a U.N. peacekeeping coordinator, said there were "very preliminary" discussions under way for a formal peacekeeping force for eastern DRC. Members of the U.N. Stabilization Mission in DRC are already on the ground monitoring the situation.
More than 100,000 people in eastern DRC were displaced by the latest violence.