Post-election violence is said to have left more than 200 people dead as world leaders try to get incumbent President Laurent Gbagbo to step down, The Guardian reported.
Opposition leader Alassane Ouattara defeated Gbagbo in November's election, but Gbagbo refused to step down, claiming election fraud. The United Nations, the United States, and the African Union recognize Ouattara as Ivory Coast's president.
Peacekeepers have so far been kept away from the alleged mass graves.
U.N. Secretary-General Ban Ki-moon telephoned Ouattara and expressed concern over reports of human rights violations.
"The secretary-general told President Ouattara that he was alarmed by the reports of egregious human rights violations," said U.N. spokesman Martin Nesirky.
The U.N. said up to 80 bodies may have been moved into a building in a pro-Gbagbo neighborhood in Abidjan, Ivory Coast's capital.
Another mass grave was believed near Gagnoa in Ivory Coast's interior, the U.N. mission in Ivory Coast said.
Nesirky said peacekeepers were "instructed to do everything possible to gain access to the affected areas both for prevention and to investigate and record the violations so that those responsible will be held accountable."
Pressure on Gbagbo is set to increase Monday when presidents from three West African countries try to meet with him.