In March 2009, two months after his inauguration as president, Barack Obama spoke directly to Iran's leaders and people. In a video message with Persian subtitles on Nowruz (Iranian New Year), he acknowledged the "serious differences that have grown over time" between the two countries, but said the US now sought engagement "grounded in mutual respect".
Obama's offer to talk was the most significant move towards reconciliation since diplomatic relations between the US and Iran were severed in 1980, after Iranian militants stormed the US embassy in Tehran in November 1979 and held 52 Americans hostage for 444 days. The Iranian government had played a discreetly supportive role during the invasion of Afghanistan in 2001 by briefing western intelligence agencies on al-Qaeda and promising to search for US pilots shot down over its territory. Its reward was a place in George W Bush's "axis of evil", which convinced many Iranians that détente with the US was impossible.
Through an aide, Iran's president, Mahmoud Ahmadinejad, welcomed "the interest of the American government to settle differences", but said Washington "should realise its previous mistakes and make an effort to amend them". And then, nothing.
Some commentators believed the domestic turmoil following Iran's presidential elections on 12 June last year would make a weakened regime more amenable. They were wrong. In July, the US secretary of state, Hillary Clinton, warned Tehran that America would offer a nuclear umbrella to its Middle Eastern allies if the Islamic Republic got the bomb. In September, Iran announced a new enrichment plant at Fordow, near the city of Qom. At the G20 summit later that month, Tehran's vague proposals for "dialogue", with no mention of its nuclear programme, did little to alleviate growing international fears.
In October, at meetings with the five permanent members of the UN Security Council (plus Germany), Iran caused confusion over its promise - or not - to export its uranium for enrichment abroad. Then, on 7 February, Ahmadinejad ordered the national atomic energy agency to begin enriching uranium to 20 per cent (an increase from 3.5 per cent), in order to make the fuel it claims is desperately needed for its nuclear reactor in Tehran. Even though this increase brings the level nowhere near the 90-odd per cent required for production of nuclear warheads, diplomatic outrage followed, and western powers, led by the US defence secretary, Robert Gates, called for tougher sanctions against Iran.
One recent Sunday afternoon, I visited Ali Asghar Soltanieh, Iran's ambassador to the International Atomic Energy Agency, in Vienna, where the agency has its headquarters. His job (a post he has held twice, for a total of 23 years) requires him to explain and defend Iran's nuclear programme to a sceptical audience. He must be one of the most overworked diplomats in the world.
We discussed Iran's nuclear ambitions (they are peaceful, he said); what the programme means to the country (self-sufficiency); and what its purpose is (technological advancement and energy diversification). Of Obama he said: "The world was fed up with America's policy of aggression and invasion based on bloodshed. This could not survive, so the American people decided that they had to make a change. President Obama is the result of the augmentation of the world's hatred against the United States."
Is he an improvement? "Well, as a result of a demand for change, he came with a slogan for change. Whether he can translate those words into action, we will have to see. So far, Obama has been unable to deliver, and on occasion has resorted to using the same language of threats as George W Bush. This is very disappointing."
Soltanieh speaks with the intensity of one who feels his country has been treated unjustly and its position misrepresented. "I have told many western friends that they need a training course on Iranian culture. This language of threats is the language used to animals, and therefore whoever uses it is condemned by us as uncivilised. It is a colonialist mentality. By threatening Iran with the Security Council, with sanctions, with military action, you are just making life more difficult for yourself - it doesn't work."
He insisted that Iran is "still co-operative". But, he added, "as they won't give us the fuel, unfortunately we have to make it ourselves - go to 20 per cent enrichment".
The two sides seem as far apart as ever.
In Washington, DC, Bruce Riedel, a former CIA operative who worked on Obama's presidential campaign, told me the current US government is determined to solve the problem, and has been from the start. "During the campaign, there was much conversation about how the new administration, once in office, would begin dealing with Iran. There was a consensus that the Bush policy of not engaging directly was a failure," he said. "A new approach was absolutely essential; and that approach required direct, face-to-face US-Iranian contacts."
The problem is that, after 30 years of mutual antipathy, relations are poisoned by a severe lack of trust. Iran says its nuclear programme is for peaceful purposes; western powers and Israel are not so sure.
Nicholas Burns, a former US undersecretary of state for political affairs who is now a Harvard professor of the practice of diplomacy and international politics, said he had "never met a diplomat or official from another country, whatever that country might be, who doubted that Iran was seeking a nuclear weapons capability. It is a given in international politics today."
And there is a further problem. While this nuclear programme, or rather the spectre of an Iranian bomb, is something that Washington alone has the power to resolve, it is not a bilateral issue: anxieties about Tehran's intentions extend across the Middle East and Europe.
In Tel Aviv, I met Avi Dichter, a former head of Israel's internal security service, Shin Bet. He is a Knesset member for the centrist Kadima party and, like many Israelis, he believes that Iran poses an "existential threat" to the Jewish state. "Around 70 per cent of our population is concentrated in the triangle between Tel Aviv, Jerusalem and Haifa," he said. "When you have 70 per cent of your people in such a small area, a nuclear bomb can be absolutely devastating."
Officially, the Israeli government supports negotiations, but the message is clear: patience is not endless. "Diplomacy must be tough," Dichter said, "because the alternative is a military strike against Iran."
The prospect of an attack by Israel terrifies the international community. For a start, it would probably fail - Iran's nuclear facilities are buried underground, geographically dispersed and well protected - but the political cost could be horrific. With American troops stationed in the Persian Gulf and Iraq, the US would suffer the brunt of retaliation by Iran.
Confronted with this possibility, and the stalled negotiations, it is perhaps understandable that the US is contemplating a hardening of sanctions. Riedel outlined the current thinking in Washington. "Senior people," he told me, "working on non-proliferation in this administration understand that going through the process of engagement and then through the process of sanctions is important to build global support for trying to brand Iran's nuclear programme as something that cannot be allowed." The Arab world fears a nuclear Iran and the impact it would have on the region but doesn't say so publicly. Tough sanctions require coalitions: building these is difficult in the Middle East.
On a recent trip to Cairo, I spoke to Nasser Aldeen, adviser to the secretary general of the Arab League, Amr Moussa.
“The Arab countries do not want to think about what could happen in the future in Iran," he said. "There are many people who say that Israel has 100 or 200 nuclear warheads. This is something that affects the Middle East. A region that wants stability does not want there to be any weapons of mass destruction in the area."
Last year, Israel signalled that it had a potential "second strike" capability in the Dolphin-class submarines that it sent through the Suez Canal into the Persian Gulf; this would have been possible only with Cairo's consent. The Arab world is afraid of Iran, but doesn't say so publicly because many of its people are delighted that there is a Muslim nation willing to face down the west. If Obama is too strident in his confrontation with Iran, he may lose the Arab goodwill he has courted over the past year - not least with his Cairo speech in June 2009, in which he called for a "new beginning between the United States and Muslims".
Acutely aware of his country's image problem, particularly on the nuclear issue, Obama also used a speech in Prague last April to call for a nuclear-free world. This played well in capitals across the Middle East, but Iran remains sceptical. "The country occupying Iraq and Afghanistan is calling for a world without nuclear weapons, when they have the highest number of nuclear warheads," Soltanieh told me that afternoon in Vienna. "So we question whether they genuinely mean what they say."
He paused, and then said, wearily: "During the eight years of Saddam's war, we lost thousands of our loved ones to protect the geographical borders of Iran. Now we are protecting our scientific and moral borders. This is much more valuable. We have said that we are always ready to talk in a civilised manner. But the west just has to cope with a strong Iran, a country with thousands of years of civilisation, that is now the master of enrichment. I know it is hard for them to digest, but it is the reality. Iran will never give up enrichment - at any price. Even the threat of military attack will not stop us."
Iran is steadfast; the US is suspended between the conflicting desires of its allies. The result is stalemate. Since the elections in June, however, Iran's establishment has become increasingly fractured. This offers opportunity for the US and its allies. Ahmadinejad recently said that he would consider shifting the focus of the programme from uranium enrichment to building more nuclear reactors. If he is serious, this would open up the prospect of a deal.
Nuclear power is crucial to Iran as an alternative to consuming the oil and gas supplies which, as exports, contribute considerably to the country's wealth. But more than this, its nuclear programme has come to embody a nation's refusal to be cowed. In the words of Iran's former nuclear negotiator Hassan Rohani, the people are united in "wanting nuclear technology because the US says we can't have it". And that unity extends across Iranian society, including parts of the opposition Green Movement.
However, there is only so much internal unrest and international opprobrium that the Iranian elite can withstand. They are more pragmatic than some on the American or Israeli right believe. Iran's decision to enrich to 20 per cent should be seen for what it is - essentially a negotiating ploy from a country that needs nuclear fuel. Thirty years of not talking achieved nothing; Obama must continue to seek dialogue with Iran.