United Nations Secretary-General Ban Ki-moon called the Holocaust "the darkest chapter in history" at a synagogue service remembering the victims.
Ban wore a kipah during the Jan. 20 service at Park East Synagogue in New York City.
"We can never tolerate anybody who denies the Holocaust," Ban said in his comments, calling the Holocaust "the darkest chapter in history," according to the French news agency AFP.
During the service, Rabbi Arthur Schneier called Ban "a mensch," and said that he was a believer in "compassionate diplomacy, diplomacy from the heart," according to AFP.
Other top U.N. officials, including Israel's U.N. ambassador and the consul general of Israel in New York, attended the ceremony.
Two exhibitions on the Holocaust will open at the United Nations in the main gallery of the visitors' lobby on Jan. 25 as part of a weeklong series of Holocaust remembrance activities at the United Nations.
The official International Memorial Day is Jan. 27.