(CNN) -- U.N. Secretary-General Ban Ki-moon condemned hostile remarks toward Israel and the denial of the Holocaust in Iran Thursday.
Speaking at the Non-Aligned Summit in Tehran, the U.N. leader didn't mention the Iranian regime, but Iranian President Mahmoud Ahmadinejad has made a string of incendiary remarks in recent years about Israel's existence and the Nazi Germany extermination of Jews last century.
"I strongly reject threats by any member state to destroy another or outrageous attempts to deny historical facts, such as the Holocaust," he said, speaking in Ahmadinejad's home turf.
"Claiming that another U.N. member state, Israel, does not have the right to exist, or describing it in racist terms, is not only utterly wrong but undermines the very principles we have all pledged to uphold."
Ahmadinejad has denied the Holocaust over the years and has been a strident opponent of Israel's existence. During a recent speech in Tehran, Ahmadinejad called for unity among all human beings to remove the Zionist "black stain" from the human society, Iranian media reported.
"I urge all (Non-Aligned Movement) members to work within the principles of the U.N. Charter to resolve disputes peacefully," Ban said. "But it is not sufficient to focus on lowering tensions between (Non-Aligned Movement) countries, as important as that is. We must prevent conflict between all U.N. member states."
Ban had been discouraged by the United States from attending the meeting, seen as a propaganda stage for the Iranian regime.
But the secretary-general says the United Nations has a "close history" and shared principles with Non-Aligned Movement, made up of nations that claim not to be aligned with any world power.
"Assuming the leadership of the NAM provides Iran with the opportunity to demonstrate that it can play a moderate and constructive role internationally. That includes responsible action on the nuclear program which is among the top concerns of the international community," Ban said.
Iran's nuclear aspirations have been a top issue for the United States and other Western nations.
The United States, along with other permanent members of the U.N. Security Council, have engaged in discussions with Iran this year about its nuclear program. Western countries believe Tehran is intent on building nuclear weapons. Iran claims the program is only for civilian medical and energy purposes.
"For the sake of peace and security in this region and globally, I urge the government of Iran to take the necessary measures to build international confidence in the exclusively peaceful nature of its nuclear program," Ban said.
Earlier at the summit, Iranian Supreme Leader Ayatollah Ali Khamenei defended his country's right to produce nuclear energy for peaceful purposes.
"The Islamic Republic of Iran considers the use of nuclear, chemical and similar weapons as a great and unforgivable sin," Khamenei said.
"This does not mean forgoing our right to peaceful use of nuclear power and production of nuclear fuel," he said. "On the basis of international laws, peaceful use of nuclear energy is a right of every country."
While defending his nation's nuclear program, Khamenei took jabs at the United States.
"A bitter irony of our era is that the U.S. government, which possesses the largest and deadliest stockpiles of nuclear arms and other weapons of mass destruction and the only country guilty of its use, is today eager to carry the banner of opposition to nuclear proliferation," he said.
Earlier this month, the U.S. Congress passed a package of sanctions aimed at Iran's nuclear program.
Khamenei also criticized the U.N. Security Council, calling it a "flagrant form of dictatorship" that is not fair to some nations.
"The U.N. Security Council has an illogical, unjust and completely undemocratic structure and mechanism," he said. "... It is through abusing this improper mechanism that America and its accomplices have managed to disguise their bullying as noble concepts and impose it on the world."
The summit is scheduled to end Friday.
CNN's Lateef Mungin, Joe Sterling and Richard Roth contributed to thsi report