Outline of nuclear deal begins to emerge before UN debut as president says people should 'be completely free in private life'

President Hassan Rouhani has signalled his intention to lead a new Iran on to the international stage at the United Nations next week, laying out a manifesto for personal freedom at home and compromise abroad.

"We want the people in their private life to be completely free," the newly elected president told NBC News, after a string of prisoner releases. He also pledged to create a citizens' rights commission "in the near future".

"In today's world, having access to information and the right of free dialogue and the right to think freely is the right of all people, including the people of Iran," Rouhani said.

Rouhani also vowed that Iran would never seek nuclear weapons and insisted his government had "complete authority" to resolve the 11-year international impasse over Iran's nuclear aspirations.

The bold rhetoric, backed up by a series of concrete steps taken with the apparent backing of Iran's supreme leader, Ali Khamenei, has raised hopes of major diplomatic breakthroughs in the coming months, affecting the long-stalled nuclear negotiations and perhaps the Syrian conflict too.

Optimism before Rouhani's debut on the world stage at the UN general assembly on Tuesday is tempered among western diplomats by uncertainty over the readiness of Khamenei to accept significant limits on the nuclear programme, long cherished by the regime as central to national prestige and dignity.

Observers of the long deadlock between Iran and international community over Iran's uranium enrichment voiced concern over the west's ability to respond to Rouhani's overtures quickly enough to bolster his still-fragile control over the machinery of government

"I think he has significant leeway to reach a deal, but that this window of opportunity is limited. The approach must be step-by-step, but we need to see tangible progress in the months to come, otherwise hardliners will undercut Rouhani," said Mohammad Ali Shabani, a Tehran-based analyst.

Rouhani, a Glasgow-educated pragmatist and former nuclear negotiator who decisively won presidential elections in June, has orchestrated a charm offensive before the general assembly, which his government clearly views as a critical moment for escaping the isolation exacerbated by his mercurial predecessor, Mahmoud Ahmadinejad.

The new foreign minister, Mohammad Javad Zarif, is due to meet the British foreign secretary, William Hague, and the EU foreign policy chief, Lady Ashton, on Monday, to lay the groundwork for Rouhani's general assembly speech the next day.

But Zarif arrived in New York five days early to network with diplomatic contacts largely made when he was ambassador to the UN a decade ago, under Iran's last moderate government. At a banquet on Wednesday, the deputy UN secretary general, Jan Eliason, reportedly hailed his quarter-century friendship with Zarif and welcomed Iranian willingness to cooperate.

Iranians are hopeful Rouhani will liberalise access to social media and websites. Photograph: Hasan Sarbakhshian/AP

Over the past few weeks, Iranian officials have sent signals that they would be open to significant compromises on the nuclear programme that could pave the way to a deal.

The head of the Iranian atomic organisation, Ali Akbar Salehi, suggested recently the country could accept the "additional protocol" of the International Atomic Energy Agency, which allows inspectors to visit sites other than those declared by the government as nuclear-related. That step is seen as essential by the IAEA in strengthened international confidence that there is no covert weapons programme running in parallel with the civil nuclear project.

Diplomats and observers said the contours of a potential breakthrough nuclear deal were increasingly clear. Iran would agree to limit enrichment of uranium to 5% purity (good enough for nuclear power stations, but far short of weapons grade), get rid of its stockpile of 20%-enriched uranium, and agree to the additional protocol.

In return, the west would lift a significant part of its sanctions regime and recognise Iran's right to enrich uranium as part of a complete nuclear fuel cycle.

Shabani said he thought such a package would be acceptable to Tehran. However, it could still be extremely difficult to reach a deal given a long history of mutual distrust. The sequencing of mutual concessions would be subject of delicate negotiations as would be their irreversibility.

In such talks, the White House would be hamstrung by the fact that most US sanctions are in the gift of Congress over which President Obama has limited sway.

"In Washington there is a question of who is in charge of Iran policy," said Jim Walsh, an expert on the Iranian nuclear programme at the Massachusetts Institute of Technology.

Obama could use presidential waivers to suspend sanctions, but those waivers could subsequently be overridden by Congress, and would be consequently be of limited value to Tehran.

"This is going to question worth watching. If we go down this path and we can't deliver we are going to confirm all of Iran's worst suspicions about double-dealing," Walsh said.For the time being, Rouhani appears to have the supreme leader's backing. Earlier this week, Khamenei, talked about the virtues of "heroic leniency" in diplomacy in a speech to the revolutionary guard that was widely seen as providing Rouhani the political space to make a nuclear deal.

Rouhani stressed the point in his NBC interview, saying: "In its nuclear programme, this government enters with full power and has complete authority. We have sufficient political latitude to solve this problem."Observers fear that backing could evaporate if Rouhani is unable to deliver swift economic improvements in the form of loosening the sanctions which straitjacket on Iran. There are clear signs on the domestic stage at least that the supreme leader has delegated real power to the new president which Rouhani is rapidly putting into effect.

Iranians have seen an almost daily series of changes that add up to a steady transformation of society since Rouhani's inauguration last month. A new pro-reform and pragmatic cabinet has restructured the senior management levels of major ministries, especially in the oil ministry, an important lever of power in a hydrocarbon-dependent economy.

Last week, the ministry for culture and Islamic guidance ordered the re-opening of House of Cinema, home of the country's independent film industry, which was shut down under Ahmadinejad.

Web users in Iran report a significant improvement in the internet speeds and availability as several new ministers like Zarif have embraced Facebook and Twitter, triggering speculation that the authorities will lift the filtering of social media.

The release this week of a number of prominent activists – including the human rights lawyer Nasrin Sotoudeh – has followed Rouhani's appointment of Seyed Mahmoud Alavi as intelligence minister. He has pledged to stay out Iranians private lives, and invited Iranians who left the country after the 2009 disputed elections to return provided they had not committed a criminal offence.

Restrictions on local news agencies and newspapers seem to have eased recently with a few going as far as breaking the taboo on reporting the plight of political prisoners or the house arrests of opposition leaders.

Thursday's headline in Tehran reflected the current feel-good atmosphere in Tehran. Etemaad, a reformist newspaper, carried a headline saying: "Dismissal, freedom and championship," referring accordingly to the dismissal of the hardline head of Iran's Azad University, the release of prisoners and a victory of Iran's national freestyle wrestlers in world championship.

Jafar Tofighi, the new acting minister of science, research and technology, has also replaced hardliners at the top of Iran's major universities and signalled that students previously ejected from universities as a result of political activism can now re-register.

Lawyer Nasrin Sotoudeh smiles at her home in Tehran, after being freed after three years in prison on politically motivated charges. Photograph: Behrouz Mehri/AFP/Getty Images

Ali Alizadeh, an Iranian political analyst based in London, said the governments reform were rooted in a new spirit of pragmatism forged by sanctions, deep social and political discontent and the weakening of Bashar al-Assad's regime in Syria.

"The supreme leader … has implicitly restrained the Iranian hardliners and has given theological licence to retreat from what previously held the ideological edifice of the regime together: nuclear programme and lack of relations with the US," Alizadeh said.

"Unlike the last three governments, for the first time, the supreme leader, the government, major political factions of the regime and significant parts of the Iranian people are in temporary unison over a few important issues."

Mohammad-Taghi Karroubi, son of the opposition leader under house arrest, Mehdi Karroubi, said the prisoner releases would strengthen Rouhani's position at the UN and give him more credibility. He did not think his father or fellow opposition leader, Mir Hossein Mousavi, would be released immediately but thought the steps taken by the government so far paved the way for their freedom.

Rouhani's coups

Softened diplomacy

He heralds improved diplomatic relations with the west by an exchange of letters with Barack Obama and David Cameron in early August. Both Iran's supreme leader and Rouhani subsequently strike a newly conciliatory tone, seeming to signal Iran's readiness for a fresh chapter in diplomacy.

Moderates promoted

Rouhani appoints a new cabinet consisting of pro-reform moderates and pragmatists, naming the veteran US-educated Iranian diplomat Mohammad Javad Zarif as foreign minister. Several key officials belonging to Mahmoud Ahmadinejad's era are dismissed from posts in major ministries.

Censorship eased

On 12 September Iran's independent House of Cinema – the main film guild, shut down under Ahmadinejad – is reopened. Students previously banned from universities because of political activity are allowed to continue their education. Formerly tight restrictions on the media are eased, with some journalists reporting on the situation of political prisoners.

Women's rights advanced

Following the appointment of Marzieh Afkham as Iran's first female foreign ministry spokesperson and two women as deputies to the prime minister, 24-year-old Shirin Gerami this week became the first Iranian woman to race in triathlon under the Islamic republic's flag.

Political prisoners released

On Wednesday leading human rights lawyer Nasrin Sotoudeh is released from jail, along with a number of other prominent political activists. This follows the easing of the terms of the house arrest of opposition leaders Mir Hossein Mousavi and Mehdi Karroubi, allowing them more frequent family visits.