Piling onto the bandwagon of people making strong and controversial statements at the Nonaligned Movement's summit in Teheran, Iran's Supreme Leader Ayatollah Khamenei said that his country never has and never will pursue nuclear weapons, and that the use of nuclear weapons is "a big and unforgiveable sin."

"Nuclear arms have neither provided security nor boosted political power," he said.

But neither will Iran relnquish its nuclear development program.

"I declare that the Islamic Republic of Iran has never been after nuclear weapons and it will never abandon its right for peaceful use of nuclear energy," he said during the summit's opening session.

Khamenei also singled out the United States for having the largest stockpile of nuclear weapons in the world.

"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.

"Our motto is: Nuclear energy for all, nuclear weapons for none," he said.

However, on Thursday, the International Atomic Energy Agency (IAEA), the United Nation's nuclear watchdog, said Iran had doubled capacity at its Fordo nuclear site.

The IAEA also noted that Iran had "significantly hampered" the ability of monitors to inspect the nuclear site at Parchin.

Iran has produced 417 pounds of higher-grade enriched uranium since 2010, up from 145kg, the IAEA also said.

Under severe sanctions from the US and EU, Iran has repeatedly denied that it seeks to develop nuclear bombs.

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