"We will be in touch with the EU-3 on Monday morning so we can become fully informed about the letter's content but until we are in touch with the EU-3 we are going to withhold comment," State Department spokesperson Justin Higgins told AFP.

Iranian news agencies reported that the country's top nuclear official, Ali Larijani, had sent a letter to foreign ministers from Britain, France and Germany "insisting on the necessity of negotiations".

However, Iran was swiftly rebuffed so long as it rejects a renewed freeze on fuel cycle work.

Talks between Iran and the so-called EU-3 broke off in August when Iran resumed uranium conversion in defiance of international calls to maintain a suspension.

Officials said Iran would convert a fresh batch of uranium ore in a flagrant rejection of EU calls for a renewed freeze on such activities that prompted an EU diplomat to reject the Iranian request out-of-hand.

"If these reports were true this would be another step that would take Iran in the wrong direction and serves only to further isolate Iran from the international community," Higgins said.