Russian Deputy Foreign Minister Sergei Ryabkov said last week that Iran could stop work on uranium centrifuges to shield it from oil sanctions from the European Union set to go into effect July 1.
"We need to study this proposal and to establish on what basis it has been made," said Iranian Ambassador to Russia Mahmoud-Reza Sajjadi, in a statement to Bloomberg News.
U.S. State Department spokeswoman Victoria Nuland dismissed Sajjadi's comments on nuclear concessions, however.
"Frankly, what's most important is what Iran says and does at the negotiating table," she said.
The International Atomic Energy Agency said Iran increased the number of centrifuges at its Natanz facility 14 percent to 9,156. The country tripled production of uranium enrichment to 31 pounds per month by November, the IAEA said.
Iran said it expects to meet with members of the IAEA in Vienna in mid-May. Multilateral talks are expected in Baghdad next month as well.