Iranian state television on Tuesday quoted Mahmoud Ahmadinejad, the Iranian president, as saying that Tehran would not "step back" on its decision to resume nuclear fuel work.
"Our country will go forward on the nuclear path with patience, wisdom and planning," the president was quoted as saying after a parliament session on the state budget.
"We will not make a step back on our path," he said, adding that he had informed the UN atomic agency of Iran's intent in a letter.
Iran's student-run news agency ISNA further quoted Ahmadinejad as rejecting Western influence on Iranian policies because "research has no restrictions or red lines".
"We cannot base our national interest on their policy," he said.
Mohammad Saidi, the deputy head of Iran's atomic energy agency, also said the UN nuclear watchdog has already been informed of the step, which risks creating further strains in talks with European negotiators.
Tehran is suspected of secretly
developing atomic weapons
"In a letter, the IAEA (International Atomic Energy Agency) has been informed that Iran will start research on the technology of nuclear fuel in a few days, with the cooperation and coordination of the agency," Saidi told state television.
"We think our experts have undergone lots of losses during this period (of suspension). Many of our researchers have lost their jobs," he added.
Saidi did not specify exactly what the research concerned, but said that the Islamic republic had "voluntarily" suspended such activities for around "the past two-and-a-half years".
This timescale would correspond to the date when Iran announced in October 2003 that it was temporarily suspending uranium enrichment, a process that can be used to create nuclear fuel for reactors and also the cores of atomic bombs.
Diplomats have said that were Iran to resume enriching uranium it would deal a fatal blow to the negotiating process, already fragile after Tehran restarted uranium conversion last year - the precursor step to enrichment.
In a statement confirming receipt of the letter, the IAEA said its director general Mohammed ElBaradei "recalls the importance placed by the IAEA Board that Iran maintains its suspension of all enrichment-related activity as a key confidence building measure".
"Our country will go forward on the nuclear path with patience, wisdom and planning"
The IAEA said it was seeking clarifications from Iran as to the "implications" of the decision.
France on Tuesday called on Iran to reverse its move, saying if Iran was to observe a suspension on enrichment it also had to halt research.
Meanwhile, a delegation from Moscow is to visit Tehran on Saturday amid continued Russian efforts to break the deadlock between Iran's insistence on maintaining its right to enrichment and EU demands it renounces the practice.
"A Russian delegation led by Deputy Foreign Minister (Sergei) Kisliak, is due to come on 7 January to discuss the Russian proposal," said Foreign Ministry spokesman Hamid Reza Asefi.
Moscow has suggested allowing Iran to conduct uranium enrichment in Russia, giving it access to the nuclear fuel cycle while guaranteeing its nuclear programme is for peaceful purposes only.
However Asefi reaffirmed Iran would not consider the offer unless it acknowledges the country's right to conduct uranium enrichment operations in Iran, so far the key sticking point in negotiations with the European Union.
"It's not a structured proposal it is still an idea, we have to discuss it. There are ambiguities but if it says that enrichment can only happen in Russia it's not acceptable, but if it's a parallel and complementary plan we will consider that."
The United States accuses Iran of trying to master the civil nuclear fuel cycle as a cover for a military programme to obtain atomic weapons - a charge vehemently denied by Tehran.