Serbian President Tomislav Nikolic described the 1995 massacre at Srebrenica as a "great crime" but said it wasn't "a premeditated act" or "an act of genocide."
Mark Toner, a spokesman for the U.S. State Department, said Washington "deplores" statements made by Serbia's newly elected president.
"Genocide in Srebrenica is not a subjective determination -- it is a defined criminal act which the International Criminal Tribunal for the former Yugoslavia has confirmed in final and binding verdicts in multiple cases," Toner said in a statement.
Former Bosnian Serb military commander Ratko Mladic was accused last month at a tribunal in The Hague, Netherlands, of helping orchestrate an ethnic cleansing campaign in Bosnia in the 1990s.
Prosecutor Dermot Groome said Mladic, as commanding general of Serb forces, orchestrated the 1995 massacre at Srebrenica and bombing campaigns in Sarajevo.
The Srebrenica massacre in July 1995 left more than 8,000 Muslim teenagers and men dead. The event is considered the worst massacre in post-World War II European history.