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(CNN) -- The Iranian Supreme Leader Ayatollah Ali Khamenei defended his country's right to produce nuclear energy for peaceful purposes during a fiery speech Thursday.

"The Islamic Republic of Iran considers the use of nuclear, chemical and similar weapons as a great and unforgivable sin," Khamenei said.

He highlighted his nation's commitment to a "Middle East free of nuclear weapons" during the speech at the Non-Aligned Movement summit in Tehran, Iran.

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"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 U.S..

"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. The United States, along with other permanent members of the U.N. Security Council, engaged in discussions with Iran this year about the nuclear program that many Western countries fear has a clandestine military dimension to it.

Iran claims the program is only for medical and energy purposes.

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 Non-Aligned Movement is made up of some 120 nations that claim not to be aligned with any world power. The summit is scheduled to end Friday.