Ahmadinejad, who has sparked international outcry by referring to the killing of 6 million Jews in World War II as a "myth" and calling for Israel to be "wiped off the map," launched another verbal attack on the Jewish state.
"Thanks to people's wishes and God's will, the trend for the existence of the Zionist regime is downwards, and this is what God has promised and what all nations want," he said. ( Watch an ex-KKK leader say why he's at the conference )
"Just as the Soviet Union was wiped out and today does not exist, so will the Zionist regime soon be wiped out," he added.
His words received warm applause from delegates at the Holocaust conference, who included ultra-Orthodox anti-Israel Jews and European and American writers who argue the Holocaust was either fabricated or exaggerated.
His remarks were condemned in Washington, where U.S. State Department spokesman Sean McCormack told reporters that the Iranian president's behavior was "despicable" and called his comment "absolutely outrageous."
The Vatican, Germany and the European Commission added their voices Tuesday to others -- such as the United States and Israel -- who have condemned the Tehran meeting.
Iran says it organized the conference to shed light on the reasons behind the formation of the state of Israel after World War II and to allow researchers from countries where it is a crime to question the Holocaust to speak freely.
"Iran is your home and is the home of all freedom seekers of the world," Ahmadinejad said. "Here you can express your views and exchange opinions in a friendly, brotherly and free atmosphere."
He urged countries where Holocaust denial is a crime to respect freedom of speech and not to take action against any of the conference participants on their return.