“In his letter the president indicated that the US is ready to resolve the nuclear issue in a way that allows Iran to demonstrate that its nuclear program is for exclusively peaceful purposes,” said White House spokesman Jay Carney.

“The letter also conveyed the need to act with a sense of urgency to address this issue because, as we have long said, the window of opportunity for resolving this diplomatically is open, but it will not remain open indefinitely,” Carney said.