Mohammad Saeedi, Deputy Head of the Atomic Energy Organization of Iran, said Iran's nuclear program had suffered significantly from its research suspension during the past two and a half years and that it could no longer keep its scientists from proceeding.
Saeedi did not say what kind of nuclear fuel research Iran was planning to resume, but he said plans did not include uranium enrichment.
The announcement was certain to raise further concerns in the United States and among its European allies who believe Iran is moving toward production of nuclear weapons. Tehran says the program is for electricity generation.
In Vienna, Mohamed Elbaradei, the head of the International Atomic Energy Agency, said Iran also had told his agency of the decision on Tuesday.
The Iranian mission to the IAEA told the agency that Iran "has decided to resume from 9 February 2006 ... R&D (research and development) on the peaceful nuclear energy program which has been suspended," ElBaradei told the IAEA's 35 board member nations in a restricted document made available to The Associated Press.
A European diplomat accredited to the agency said it was too early to evaluate the significance of the move and whether it would scuttle talks planned for later this month between Iran and France, Britain and Germany on behalf of the European Union.
The EU has previously said that any decision by Iran to resume work on its uranium enrichment program would be "the red line" that would mean an end to European attempts to negotiate differences with Iran over its nuclear program and revive attempts to have it taken before the U.N. Security Council for violating the nuclear nonproliferation treaty.
But the diplomat, who demanded anonymity in exchange for discussing EU strategy, said the Europeans would want to have details of what precisely Iran wanted to do before making a decision on future talks.
The West has long opposed Iran's enrichment of uranium because the process can produce fuel for atomic weapons, but Saeedi said the research now planned was not of that type.