TEHRAN — Iran’s triumphal stewardship of the Nonaligned Movement summit meeting here veered off script Thursday when the two most prominently featured guest speakers, President Mohammed Morsi of Egypt and UN Secretary General Ban Ki-moon, denounced the repression of the armed uprising in Syria, a close Iranian ally.

Syria’s foreign minister walked out in protest at Morsi’s remarks at the meeting, the largest international conference in Iran since the 1979 Islamic revolution. Iranian leaders have portrayed the meeting, attended by delegations from 120 countries, as a validation of Iran’s importance in the world and a rejection of Western attempts to ostracize it.

Ban added to the embarrassment by publicly upbraiding his Iranian hosts in his speech for threatening to annihilate Israel and for describing the Holocaust as a politically motivated myth.

“I strongly reject threats by any member state to destroy another or outrageous attempts to deny historical facts, such as the Holocaust,’’ Ban said.

In what appeared to signal Iran’s effort to avoid public friction over the Syrian conflict that would detract from the tone of the Nonaligned conference, Ayatollah Ali Khamenei, Iran’s supreme leader, opened the day with a welcoming speech that conspicuously avoided any mention of Syria. But Morsi and Ban refocused attention on it.

With the Iranian president, Mahmoud Ahmadinejad, sitting beside him, Morsi spoke of an ‘‘oppressive regime’’ in Syria and said the opposition should unite in its effort to unseat President Bashar Assad.