Iran’s leaders, seizing on perceived flexibility in a private letter from President Barack Obama, have decided to gamble on forging a swift agreement over their nuclear programme with the goal of ending crippling sanctions, a prominent adviser to the Iranian leadership has said.

The adviser, who participated in top-level discussions of the country’s diplomatic strategy, said that Obama’s letter, delivered to Iran’s new president, Hasan Rouhani, about three weeks ago, promised relief from sanctions if Tehran demonstrated a willingness to “cooperate with the international community, keep your commitments and remove ambiguities.”

A senior US official did not dispute the general outlines of the letter as described by Amir Mohebbian, an Iranian political expert and longtime adviser to Iran’s top leaders. But the official said Obama had not promised Iran quick relief from sanctions, and had steered clear of any detailed proposal.

Mohebbian and other officials and analysts said Iran was focused on getting quick relief from financial sanctions because they have cut it off from the international banking system, and in exchange might be willing to curb its nuclear enrichment program. Some in the leadership are also worried that, if nuclear talks do not yield quick results, Iran’s hard-line clerics and military men - currently sidelined - could attack Rouhani as a sellout and clip his wings.

The Iranian leadership was encouraged by what was described as Obama’s offer to conduct face-to-face talks, which they prefer to the more bureaucratic and lengthy negotiating process with a group of five major world powers, Mohebbian said.

The one-and-a-half-page letter, which the Iranian president answered with a letter of similar length, has kindled hopes that the international charm offensive Iran began after Rouhani’s election in June may produce a genuine diplomatic breakthrough. But the differing interpretations of Obama’s letter in Tehran and Washington are a reminder of the political hurdles and the legacy of mistrust that both sides will have to overcome in negotiating a deal.

The US official said Obama had congratulated Rouhani on his election, and characterized the vote as an opportunity for change. But on sanctions, the official said, the Iranians were inferring relief from the president’s more general pledge to resolve issues and move forward. And while Obama was open to direct talks, the official said, they would not necessarily be leader to leader.

The Iranian reaction to the letter provides critical insight into a decisive and unexpected shift in strategy by the moderate new president as Iran struggles to restore vitality to its economy and undo years of hostile relations with most of the world under the former president, Mahmoud Ahmadinejad.

The overtures to the United States are part of a flurry of steps altering the trajectory of the Iranian state, including domestic liberalisations and returning the politically powerful military to the barracks - for now. Those actions, along with the changed diplomatic tone, have convinced some experts that the changes are more than cosmetic.

Rouhani will present Iran’s new face to world next week with an address to the UN General Assembly, an evening speech to the Council on Foreign Relations and the Asia Society, and a television interviews with Charlie Rose and CNN. In an opinion article published in The Washington Post on Friday, Rouhani said world leaders should “seize the opportunity presented by Iran’s recent election.”

“I urge them to make the most of the mandate for prudent engagement that my people have given me and to respond genuinely to my government’s efforts to engage in constructive dialogue,” he wrote. Sceptics were quick to point out that Obama has reached out to Iran before. Having promised as a candidate to extend an olive branch to old enemies, he sent a letter early in his first term to the country’s supreme leader, Ayatollah Ali Khamenei, proposing a new diplomatic chapter. In his reply, Khamenei did not take Obama up on his offer.

Their correspondence was cut short after Iran’s disputed presidential election in June 2009 unleashed a popular uprising. The ensuing bloody crackdown all but snuffed out diplomacy for the next year. Ahmadinejad, re-elected as president, wrote a lengthy letter to Obama in 2010, but it did nothing to break the diplomatic ice.

This time Obama’s letter found a receptive audience, which apparently, and crucially, includes for the first time Khamenei. Mohebbian said he had been present at an official meeting of the leadership at which the letter was read aloud and discussed by someone from “the highest levels” of Iran’s political establishment, terminology that usually describes the office of the supreme leader.

Best opportunity

Iran’s leaders are apparently convinced that the next six months, before campaigning begins for parliamentary elections in March, represent the best opportunity to reach a nuclear agreement in over a decade, Mohebbian said.

The leaders considered the tone of Obama’s letter a very promising sign, and paradoxically, they view what they see as America’s declining regional influence as a positive. Rouhani has publicly applauded Obama’s decision to refrain from striking Syria for its poison gas attack on its own civilians.

Mohebbian said Khamenei had been growing concerned about the future of the revolution, with so many of its founders aging. In particular, he wants to settle the nuclear issue and ease tensions with the United States.

“It is the leader who decides on the possibility, scope and extent of potential talks with the US,” said Mohebbian. He emphasised that Khamenei was in excellent health, “But we need him to reach consensus within our system, he feels this is the moment to try and solve this problem.”

The leadership is also desperate to escape the withering financial sanctions imposed in recent years, particularly the ban on Iranian money transfers through the SWIFT system. It can live without oil sales, analysts have said, but not without the ability to transfer money.

Mohebbian said Iran is hoping the White House will lift some sanctions as a gesture to show its seriousness about the talks. “We particularly want to be readmitted to the SWIFT system,” he said.

He and other analysts warned that, while Iran’s political establishment fully agrees that talks are worth trying, the consensus could break down within months if there are no results. “The world must know that time is not unlimited for solving the nuclear problem,” Rouhani said in his first live interview on Iranian state television, on Sept. 10.

At the White House, where Obama has long sought a rapprochement with Iran but been repeatedly frustrated, officials share the sense that this time may be different. “Rouhani is sending signals he wants to deal,” said Dennis B. Ross, a former adviser to Obama on Iran. “He wants to end the sanctions and knows he does not have a lot of time to deliver - Iranian presidents have some space in their first year and then it declines.”