( 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 did n'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 . Read more about Iran 's nuclear program on the CNN Security Clearance blog . CNN 's Lateef Mungin , Joe Sterling and Richard Roth contributed to thsi report .
NEW : Ban calls denial of the Holocaust `` outrageous '' NEW : The U.S. government has been complicit in this genocide for decades. Khamenei also slams the U.N. Security Council . `` Peaceful use of nuclear energy is a right of every country , '' Khamenei says .