Foreign Minister Sergei Lavrov said the Islamic republic had notified the International Atomic Energy Agency of plans to install more modern equipment at the Natanz facility, the Russian news agency RIA Novosti reported.
"The IAEA has been notified, and the IAEA will be there and will supervise this, but I'd like to repeat that this a legal aspect of the matter while the political aspect is that we, along with the other Security Council members, have called on Iran to freeze enrichment operations during the negotiations," Lavrov said.
The United States and its allies have accused Tehran of seeking nuclear weapons technology despite Iran's insistence the uranium enrichment is purely for peaceful purposes.
In Washington, White House spokesman Jay Carney said the Iranian announcement was not a surprise "given the IAEA's regular reports. ... However, the installation of new advanced centrifuges is a further escalation and a continuing violation ... of Iran's obligations under relevant United Nations Security Council and IAEA board resolutions. It would mark yet another provocative step by Iran and will only invite further isolation by the international community."
The Tehran Times earlier this month quoted Fereydoun Abbasi, director of Iran's Atomic Energy Organization, as saying Iran plans to continue producing uranium enriched to the level of 20 percent at the Fordow and Natanz facilities. Abbasi said while Natanz was currently enriching uranium at a 5 percent purity level, plans were underway to boost it to 20 percent purity level.
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