French Foreign Minister Philippe Douste-Blazy urged Tehran to reverse its decision and said France is "seriously concerned " by the development.
White House spokesman Scott McClellan said Iran might be referred to the UN Security Council if it goes ahead with its plans.
Germany's Foreign Minister Frank-Walter Steinmeier said Iran's decision to resume research on the nuclear fuel cycle cannot remain "without consequences."
"You have also heard that the Iranians have announced they will break the seals [on uranium processing equipment], in order to develop their enrichment activities. That would breach the agreements we made in Paris with France, Great Britain, and Iran itself. That cannot be left without consequences," Steinmeier said.
Germany, France, and Britain make up the troika that is engaged in negotiations with Iran to ensure that the country's nuclear program is peaceful.
Earlier today, Iranian government spokesman Gholam Hossein Elham said Iran would resume the research under the supervision of the International Atomic Energy Agency.
The announcement came after talks between Russia and Iran on a proposed compromise to end the row over uranium enrichment broke off without result.
RFE/RL Iran Report
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