Ali Asghar Soltanieh angrily rejected the documents as "forgeries"
The UN's nuclear watchdog has been told Iran may have continued secret work on nuclear weapons after 2003, the date US intelligence suggested the work ceased.
A US National Intelligence Estimate released last December said Tehran had frozen its atomic programme in 2003.
But documents presented to the International Atomic Energy Agency (IAEA) suggest the work continued.
Ali Asghar Soltanieh, Iran's ambassador to the IAEA, angrily dismissed the documents as "forgeries".
Simon Smith, Britain's ambassador to the IAEA, said material presented to the IAEA in Vienna came from multiple sources and included designs for a nuclear warhead, plus information on how it would perform and how it would fit onto a missile.
"Certainly some of the dates that we were talking about... went beyond 2003," he said.
No credible assurances
The material was presented to the agency's 35-nation board by the IAEA's head of safeguards, Olli Heinonen, in a closed-door meeting on Monday.
The permanent members of the UN Security Council - the US, UK, China, France and Russia - are meeting in Washington to discuss the possibility of imposing further sanctions on Iran over its disputed atomic programme.
The IAEA released a report on Friday which said Iran was being more transparent, but had not given "credible assurances" that it was not building a bomb.
US Secretary of State Condoleezza Rice said that report bolstered a "very strong case" for a third round of sanctions over the disputed nuclear programme.
But Iranian President Mahmoud Ahmadinejad retorted that no amount of UN sanctions would deter Tehran from its nuclear path.
"If they want to continue with that path of sanctions, we will not be harmed. They can issue resolutions for 100 years," he said in a televised interview on Saturday.
Tehran insists its programme is aimed purely at generating electricity.