DUBAI (Reuters) - Iran is taking preliminary steps to design uranium fuel with a purity of 20 percent for reactors instead of having to copy foreign designs, Iran’s nuclear chief said on Sunday.

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Iran’s 2015 nuclear accord with world powers caps the level to which it is able to enrich uranium to 3.67 percent purity, well below the 20 percent it was reaching before the deal, and the roughly 90 percent that is weapons-grade.

Iran is, however, allowed to produce nuclear fuel under strict conditions that need to be approved by a working group set up by the signatories to the deal. Those conditions include ensuring that the fuel cannot be converted to uranium hexafluoride, the feedstock for centrifuges that enrich uranium.

“We have made such progress in nuclear science and industry that, instead of reverse-engineering and the use of designs by others, we can design new fuel ourselves,” state broadcaster IRIB quoted Ali Akbar Salehi, head of the Atomic Energy Organization of Iran, as saying.

“Initial measures have been started for the design of modern 20 percent fuel and we’re on the verge of (achieving) it. This product is different from the previous 20 percent fuel, and we can supply fuel to any reactor that is built like the Tehran reactor,” Salehi said.

“The Tehran reactor has so far been working with old fuel, but modern fuel can improve efficiency,” he added.

Iranian officials have repeatedly criticized delays in setting up a new European Union payments mechanism for Iranian oil exports, which are hit by U.S. sanctions. But Tehran has stopped short of moves that could jeopardize the accord.

U.S. President Donald Trump pulled out of the accord last year, arguing that it was weak because it did not halt Iran’s development of ballistic missiles or support for armed proxies abroad, and he reimposed sanctions on Iran’s vital oil export sector.

But Europe sees the nuclear deal as an important element of international security.

The EU and other remaining parties - China and Russia - have tried with limited success to preserve trade incentives for Iran to respect the deal’s nuclear limits under U.S. pressure.