Iranian President Mahmud Ahmadinejad in the past has questioned the extent of the Nazi Holocaust and said Israel should be wiped off the map.
In Washington, the U.S. State Department denounced as "disgraceful" the plans to hold the conference, which is expected to question whether the Nazis used gas chambers to kill Jews.
State Department spokesman Sean McCormack said it was "just flabbergasted" that Iranian leaders continued to deny that 6 million plus people were killed in the Holocaust.
(compiled from agency reports)