US President Barack Obama has told Iran's President Hassan Rouhani in an exchange of letters that the United States is ready to resolve its nuclear dispute with Iran in a way that allows Tehran to show it is not trying to build weapons, the White House said on Wednesday.

"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.

In an interview with NBC on Wednesday, Rouhani said the tone of the letter he received from Obama was "positive and constructive."

"It could be subtle and tiny steps for a very important future," Rouhani said, in another sign that he may be seeking a thaw in relations between Iran and the West after years locked in a standoff over Tehran's nuclear program.

The United States and its allies have imposed sanctions aimed at stopping Iran from seeking a nuclear weapons capability, but Iran has long insisted its program is for civilian purposes.

Since Rouhani was elected as president in June, he has called for "constructive interaction" with the world. The head of Iran's nuclear energy organization said on Wednesday he saw "openings" on the nuclear issue.

Obama said on Tuesday that he is willing to test the willingness of Rouhani to discuss the nuclear issue.

"There is an opportunity here for diplomacy," Obama told Spanish-language network Telemundo in an interview. "And I hope the Iranians take advantage of it."

Rouhani also told NBC's Ann Curry that his government would never develop nuclear weapons and that he has full authority to negotiate a nuclear deal with the West.

Both Obama and Rouhani plan to be in New York next week for the UN General Assembly, but the leaders do not currently have plans to meet, Carney said.

Israel's nuclear chief: Iran is stalling for time

At the annual International Atomic Energy Agency (IAEA) meeting in Vienna on Wednesday, the head of Israel's Atomic Energy Commission accused Iran of using "deception and concealment" to buy time for its nuclear program, signalling scepticism that the Islamic state's new government would agree to curb its atomic activities.

The election of Rouhani, a relative moderate, as new Iranian president has raised hopes of progress in long-stalled efforts to find a peaceful solution to the decade-old dispute over Tehran's nuclear program.



But Israel's nuclear chief said: "The picture that the Iranian representatives are portraying regarding openness and transparency of their nuclear program... stands in sharp contradiction with Iran's actual actions and the facts on the ground."

The key issue was not whether Iran has "nominated new envoys, modified its diplomatic vocabulary... but whether it is addressing seriously and in a timely manner outstanding issues that have remained unresolved for too long," Shaul Chorev told the annual meeting of the UN nuclear agency.

"So far the window of serious engagement offered by the IAEA and the international community has been grossly abused by Iran," he said.

Chorev accused Iran of "deception and concealment, creating a false impression about the status of its engagement with the agency ... with a view to buy more time in Iran's daily inching forward in every aspect of its nuclear military program".

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