Western diplomats say Iran intends to greatly increase the speed of its uranium-enrichment program.
Diplomats told the Associated Press and Reuters on January 31 that Tehran informed the International Atomic Energy Agency (IAEA) that it plans to install thousands more modern uranium centrifuges at its Natanz nuclear plant.
That could enable Iran to refine uranium two or three times faster than is currently possible.
Reuters quoted nuclear expert Mark Fitzpatrick of the London-based International Institute for Strategic Studies as saying that the new centrifuges could be "a most unfortunate game changer" depending on the numbers.
Fitzpatrick said if Iran installs a large number of centrifuges it would significantly speed up the timeline for being able to produce fissile material for nuclear weapons.
There are fears Iran intends to build nuclear weapons although Tehran insists its nuclear program is for producing energy and is entirely peaceful.
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Western diplomats speaking on condition of anonymity said Iran had notified the IAEA, the UN's nuclear monitoring agency, about its plans in a letter dated January 23.
The diplomats said the development also highlights Tehran's defiance in the face of international demands to suspend all enrichment activities. UN Security Council resolutions have imposed sanctions on Iran for refusing to stop its uranium-enrichment program.
However, Russian Foreign Minister Sergei Lavrov insisted that Iran's installation of the new uranium-enrichment centrifuges does not violate Tehran's obligations to the IAEA.
The Interfax news agency quoted Lavrov as saying that the "IAEA has been notified and the IAEA will be there and [will] supervise it."
Lavrov said the installation of the new centrifuges "is a legalistic aspect of the matter, while the political-legal aspect is that we have called on Iran to freeze enrichment operations during the negotiations."
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In Brussels, European Union foreign policy chief Catherine Ashton told reporters on January 31 that world powers "continue to try to persuade Iran" to begin talks over Tehran's nuclear program.
"You know that we are in touch with the Iranians to try and organize properly our negotiations and discussions," she said. "So, I don't say and I don't think that we should see this as anything other than a process that is going to be very important. It needs to be done properly and we need to move forward on that. So we have been saying to the Iranians that we want to propose dates and venues in order that we can get the discussions moving as quickly as possible."
The EU is brokering the talks on behalf of the United States, China, Russia, Britain, France, and Germany.
Iran and these world powers have failed to agree on a venue for the next round of talks on Tehran's nuclear program. They have blamed each other for holding up the resumption of negotiations.
A meeting proposed for January 28-29 in Istanbul was postponed. The last round of negotiations in Moscow in June ended without any breakthrough.