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.
"The research in this field will have little to do with the production of nuclear fuel," Saeedi said, adding, as the ElBaradei document confirmed, that Iran planned to inform the IAEA.
"It has been decided that the International Atomic Energy Agency will be informed today about (our) research in the field of nuclear fuel. Research will resume in cooperation and coordination with the IAEA in the next few days," Saeedi said.
Iran has come under heavy international pressure from the IAEA, the U.N. nuclear watchdog, and the West to abandon its program to produce fuel for its Russian-built nuclear reactor that is due to come on stream this year and its future nuclear power plants.
Iran has vowed it will never give up its right under the Nuclear Nonproliferation Treaty to enrich uranium and produce nuclear fuel inside the country.
While refusing to renounce the enrichment of uranium, Iran suspended many aspects of its nuclear fuel program in 2003 as a gesture of good will during negotiations with the big three European powers, Britain, France and Germany.
The negotiations collapsed in August after Iran resumed uranium reprocessing activities, a step before enrichment, at its Uranium Conversion Facility in Isfahan, central Iran.
But the two sides, but talks have so far failed to resolve the dispute. Further talks are scheduled for later this month.
Iran's decision to resume nuclear research coincided with the announcement by Asefi that Iran will reject the U.S. and European-backed Russian nuclear proposal if it sought to move any Iranian enrichment program to Russia, its northern neighbor.
"The Russian proposal is ambiguous. We have to talk to the Russians to see what are the details," Asefi told reporters.
"If it means enrichment be carried out (only) in Russia, we have said it is not acceptable. But if it is a complementary plan, we will study it," Asefi said.
Extremists within the increasingly hard-line Iranian government have denounced the Russian proposal as a "dirty trick."