The uranium fuel agreement Iran struck with Turkey and Brazil has a key technical flaw as it fails to allocate enough time to make the fuel, a Western diplomat said here Monday.

"Getting this fuel in one year is impossible. It takes at least one and a half years to have this," the diplomat told reporters.

The deal "cannot work because it is only one year and it takes more time to get the enriched uranium," said the diplomat, who asked not to be named due to the sensitive nature of the issue.

The accord calls for Tehran to ship around half its stock of low-enriched uranium to Turkey.

It would later receive a supply of more highly enriched uranium in the form of fuel it needs for a reactor that produces isotopes for medical diagnosis.

The goal is for Iran to create confidence by reducing its uranium stockpile, at least for the months is would take to produce more, below the amounts needed to process further into a bomb.

The finished reactor fuel is considered less of a proliferation risk than the low enriched uranium used to make it.

Iran's uranium enrichment activities are at the heart of fears about its nuclear program because highly enriched uranium of over 90 percent purity can be used to make an atomic bomb.

Iran has been enriching uranium up to five percent in what it says is an attempt to make low-enriched fuel for civilian power reactor use.

The fuel Iran needs for its Tehran research reactor (TRR) is just under 20 percent enriched, a level closer to weapon-grade.

On Monday, Iran formally submitted notice of the fuel swap deal with Turkey and Brazil to the UN's atomic watchdog, the International Atomic Energy Agency, in Vienna.

Delegates from the three countries handed the IAEA a letter about the May 17 deal struck in Tehran.

The agency did not immediately comment on the content of the letter but according the text of the agreement released last week Iran has "expressed its readiness to deposit its LEU (low enriched uranium - 1200 kg) within one month."

"On the basis of the same agreement the Vienna Group (United States, Russia, France and the IAEA) should deliver 120 kg fuel required for TRR in no later than one year," the May 17 text said.

The diplomat said this means that if Iran has not received its fuel in one year, it could take its low enriched uranium back from Turkey, where it is to be deposited, and so boost its stockpile.

"The uranium will be in Turkey, and the deal is that after one year they can take it back. So as we know that it will take more than one year to give them the fuel, that means that... after one year, they can take it back and then wait for the fuel to come six months later," the diplomat said.

He added: "There is something tricky there, but we will see in a year. It is still too early."

Washington-based nuclear expert David Albright said it could take two years to make the fuel and this was a "real show-stopper" for the deal.

The fuel, said Albright, would be in the form of metal plates, which have to be densely concentrated with the right uranium isotope for the level of enrichment required.

Western governments have been dismissive of the new swap deal, saying it fails to address concerns about Iran's nuclear program which Tehran insists is for civilian purposes.