Iran will never try to obtain a nuclear bomb but will not give up the pursuit of peaceful nuclear energy, Supreme Leader Ayatollah Ali Khamenei told a gathering of leaders of developing countries meeting in Tehran.

"Iran will never pursue nuclear weapons and will not give up its nation's right to peaceful nuclear energy," Khamenei told the Non-Aligned Movement summit. "Our motto is nuclear energy for all, and nuclear weapons for none."

Iran's nuclear program is suspected by the West of being aimed at developing an atomic bomb, an accusation Iran denies.

Late on Wednesday, visiting United Nations Secretary General Ban Ki-moon - also present at Thursday's speech - told Khamenei to take concrete steps to prove the country's nuclear program was peaceful.

Khamenei's at times abrasive speech on Thursday also took aim at the UN Security Council, describing it as illogical, unjust and defunct relic of the past that the United States uses "to impose their bullying manner on the world."

"They (the United States) talk of human rights when what they mean is Western interests. They talk of democracy when what they have is military intervention in other countries," he added.

Television footage before the speech showed Iranian president Mahmoud Ahmadinejad in discussion with Egyptian president Mohamed Morsy - the first Egyptian leader to visit Iran since its Islamic Revolution in 1979.

As Khamenei pledged Iran's peaceful intentions, a report emerged in The Wall Street Journal that the Iranian scientist considered Tehran's atomic-weapons pioneer, had resumed work after a break of several years.

The report was based on assertions by United Nations investigators as well as US and Israeli officials.

Western intelligence agencies have identified Mohsen Fakhrizadeh as the man responsible for Iran's nuclear weapons program. He is reportedly a senior officer in the Islamic state's elite Revolutionary Guards.

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Fakhrizadeh was named in a 2007 UN resolution on Iran as a person involved in nuclear or ballistic activities. An  International Atomic Energy Agency (IAEA) report the following year also referred to him briefly.

According to The Wall Street Journal, the IAEA believes that Fakhrizadeh has opened a nuclear weapons research facility in northern Tehran. According to the report, intelligence officials said that the scientists and military staff working at this center are the same people who were active in Iran's previous nuclear weapons research. 

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