Treaties on nuclear/chemical weapons that Iran is a signatory to:
-The Convention on the Prohibition of the Development, Production and Stockpiling of Bacteriological (Biological) and Toxin Weapons and on their Destruction
-Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction.
-Treaty on the Non-Proliferation of Nuclear Weapons
A 2007 National Intelligence Estimate report on Iran's nuclear program concluded that the Islamic State had dismantled their nuclear weapons program in 2003 and not since committed to it again.
http://www.dni.gov/press_releases/20071203_release.pdfThe Supreme Leader of Iran (the true power, not the President) Ayatollah Ali Khamenei has issued a fatwa saying the production, stockpiling and use of nuclear weapons was forbidden under Islam. The fatwa was cited in an official statement by the Iranian government at an August 2005 meeting of the IAEA.
http://web.archive.org/web/20051016053118/http://www.irna.ir/en/news/view/line-17/0508104135124631.htm