Iran's foreign minister and the European Union's foreign policy chief said a nuclear deal between Iran and six powers sealed on Tuesday heralded a new chapter of hope and was a historic moment.
“I believe this is a historic moment,” Iranian Foreign Minister Mohammad Javad Zarif told a joint news conference.
“We are reaching an agreement that is not perfect for anybody but it is what we could accomplish and it is an important achievement for all of us,” he said.
“Today could have been the end of hope on this issue. But now we are starting a new chapter of hope. Let’s build on that,” he added.
The deal will curb Iran’s nuclear programme in exchange for billions of dollars in relief from international sanctions.
The deal, which follows 18 days of intense negotiations, is designed to avert the threat of a nuclear-armed Iran and another US military intervention in the Muslim world.
Russia’s president Vladimir Putin said on Tuesday: “the world can now breathe a sigh of relief,” in a statement on the Kremlin website.
“Despite attempts to justify scenarios based on force, the negotiators have made a firm choice in favour of stability and cooperation”, he said.
Putin added that the deal will help Russian-Iranian civilian nuclear cooperation and will contribute to combating terrorism in the Middle East.
The European Union's foreign policy chief Federica Mogherini said the deal sealed in Vienna after lengthy negotiations was about more than just the nuclear matter.
“It is a decision that can open the way to a new chapter in international relations and show that diplomacy, coordination, cooperation can overcome decades of tensions and confrontations,” she said.
“I think this is a sign of hope for the entire world.”
The accord will keep Iran from producing enough material for a nuclear weapon for at least 10 years and impose new provisions for inspections of Iranian facilities, including military sites.
It also marks a dramatic break from decades of animosity between the US and Iran, countries that alternatively call each other the “leading state sponsor of terrorism” and “the Great Satan”.
The final round of talks in Vienna involved representatives from the US, UK, China, France, Germany and Russia.
The formal announcement of the so-called Joint Comprehensive Plan of Action is due to be made after the meeting.
Its completion comes after more than two weeks of often fractious diplomacy, during which negotiators blew through three self-imposed deadlines.
Mr Zarif and US secretary of state John Kerry, who conducted most of the negotiations, both threatened to walk away while trading accusations of intransigence.
The breakthrough came after several key compromises.
Diplomats said Iran agreed to the continuation of a UN arms embargo on the country for up to five more years, though it could end earlier if the International Atomic Energy Agency (IAEA) definitively clears Iran of any current work on nuclear weapons.
A similar condition was put on UN restrictions on the transfer of ballistic missile technology to Tehran, which could last for up to eight more years.
Washington had sought to maintain the ban on Iran importing and exporting weapons, concerned that an Islamic republic flush with cash from the nuclear deal would expand its military assistance for Syrian president Bashar Assad’s government, Yemen’s Houthi rebels, the Lebanese militant group Hezbollah and other forces opposing America’s allies in the Middle East, such as Saudi Arabia and Israel.
Iranian leaders insisted the embargo had to end as their forces combat regional scourges such as Islamic State. They also received some support from China and particularly Russia, which wants to expand military cooperation and arms sales to Tehran, including the long-delayed transfer of S-300 advanced air defence systems — a move long opposed by the US.
Another significant agreement will allow UN inspectors to press for visits to Iranian military sites as part of their monitoring duties, something the country’s supreme leader, Ayatollah Ali Khamenei, had long vowed to oppose.
However, access is not guaranteed and could be delayed, a condition that critics of the deal are sure to seize on as possibly giving Tehran time to cover up any illicit activity.
Under the accord, Tehran would have the right to challenge the UN request and an arbitration board composed of Iran and the six world powers would then decide on the issue.
The IAEA also wants the access to complete its long-blocked investigation of past weapons work by Iran, and the US says Iranian cooperation is needed for all economic sanctions to be lifted.
IAEA chief Yukiya Amano said his agency and Iran had signed a “roadmap” to resolve outstanding concerns.
The economic benefits for Iran are potentially massive. It stands to receive more than 100 billion dollars (€91 billion) in assets frozen overseas, and an end to a European oil embargo and various financial restrictions on Iranian banks.
Mr Zarif said the agreement was a “win-win solution.”
The nuclear deal comes after nearly a decade of international, intercontinental diplomacy that until recently was defined by failure.
Breaks in the talks sometimes lasted for months, and Iran’s nascent nuclear programme expanded into one that Western intelligence agencies saw as only a couple of months away from weapons capacity. The US and Israel both threatened possible military responses.
The US joined the negotiations in 2008, and US and Iranian officials met together secretly four years later in Oman to see if diplomatic progress was possible.
But the process remained essentially stalemated until summer 2013, when Hassan Rouhani was elected president and declared his country ready for serious compromise.
More secret US-Iranian discussions followed, culminating in a face-to-face meeting between Mr Kerry and Mr Zarif at the UN in September 2013 and a telephone conversation between Mr Rouhani and US president Barack Obama.
That conversation marked the two countries’ highest diplomatic exchange since Iran’s 1979 Islamic Revolution and the ensuing hostage crisis at the American embassy in Tehran.
Mr Kerry and Mr Zarif took the lead in the negotiations. Two months later, in Geneva, Iran and the six powers announced an interim agreement that temporarily curbed Tehran’s nuclear programme and unfroze some Iranian assets while setting the stage for Tuesday’s comprehensive accord.
It took time to strike the final deal, however. The talks missed deadlines for the pact in July 2014 and November 2014, leading to long extensions.
Finally, in early April, negotiators reached framework deal in Lausanne, Switzerland, setting up the last push for the historic agreement.
Protracted negotiations still lie ahead to put the agreement into practice, and deep suspicion reigns on all sides about violations that could unravel the accord.
In the US, Congress has a 60-day review period during which Mr Obama cannot make good on any concessions to the Iranians. US politicians could hold a vote of disapproval and take further action.
Iranian hardliners oppose dismantling a nuclear programme the country has spent hundreds of billions of dollars developing. Khamenei, while supportive of his negotiators thus far, has issued a series of defiant red lines that may be impossible to reconcile in a deal with the West.
Further afield, Israel will strongly oppose the outcome. It sees the acceptance of extensive Iranian nuclear infrastructure and continued nuclear activity as a mortal threat, and has warned that it could take military action on its own, if necessary.
The deal is a “bad mistake of historic proportions,” Israeli prime minister Benjamin Netanyahu said, adding that it would enable Iran to “continue to pursue its aggression and terror in the region”.
Sunni Arab rivals of Shia Iran have also signalled their opposition, with Saudi Arabia in particular issuing veiled threats to develop its own nuclear programme.
Agencies