Six major powers have reached a "historic" agreement with Iran on the country's nuclear programme after years of negotiations.
The EU's foreign policy chief Federica Mogherini made the announcement at a news conference in Vienna where foreign ministers had been meeting to ratify a deal that was thrashed out early on Tuesday.
Ms Mogherini said the deal provided an opportunity to open a new chapter in international relations.
As part of the deal, billions of dollars worth of sanctions are due to be lifted which will allow Iran to trade with the world in a way it has not been able to for several years.
Iran's foreign minister Mohammad Javad Zarif welcomed the deal, saying: "I believe this is a historic moment. Today could have been the end of hope, but now we are starting a new chapter of hope."
US President Barack Obama, appearing in an early morning US TV broadcast that was also shown in Iran, said that the deal will mean that Iran will destroy 98% of its stock pile of weapons grade uranium, adding that it currently has enough for 10 warheads.
He said it meant that "every pathway (of Iran's) to a nuclear weapon is cut off".
"No deal means a greater chance of more war in the Middle East," he said, and promised to veto any legislation proposed on Congress to block it."
And he added that it was a deal "not built on trust", but "built on verification" and one that that has the "full backing of the international community".
A "happy day" in the Middle East
Israel's Prime Minister Benjamin Netanyahu, who has been a long-standing critic of the talks, described the deal as a "bad mistake of historic proportions".
He said: "Iran is going to receive a sure path to nuclear weapons. Many of the restrictions that were supposed to prevent it from getting there will be lifted.
"Iran will get a jackpot, a cash bonanza of hundreds of billions of dollars, which will enable it to continue to pursue its aggression and terror in the region and in the world," he added.
Saudi Arabia, which also regards Iran as a danger in the region, said that the deal would result in a "happy day" in the Middle East if it stops Tehran getting a nuclear arsenal but will be bad if the reduction of sanctions allows the country to "wreak havoc".
In his speech welcoming the deal, Iran's President Hassan Rouhani said: Iran "never sought (and) will never seek to manufacture a nuclear weapon."
Under the deal:
- UN inspectors can request visits to Iranian military sites as part of their monitoring duties, but do not have an automatic right to visit whenever they choose.
- In the event that Iran refuses a request to visit, an arbitration board composed of Iran and the six world powers will have to decide on whether a visit should go ahead.
- Analysts say that the lack of an automatic right to visit is likely to be seized upon by critics, as it could give Tehran time to cover up any non-compliance by the time a visit takes place.
- Missile sanctions will not be lifted for another eight years and a general weapons embargo will remain in place for another five years unless the UN Security Council approves an import.
- Iran will slash by around two-thirds the number of centrifuges from around 19,000 to 6,104 and will stick at this number for 10 years.
- In the event that Iran breaches the agreement, a 'snapback' clause is in place that will allow sanctions to be reinstated within 65 days of Iranian non-compliance.
- A roadmap has been drawn up to tackle remaining issues, which will be resolved by the end of 2015, including the issue of access to the Parchin military base.
The West has long been concerned that Iran holds ambitions to build a nuclear bomb. Tehran says its nuclear programme is purely to generate energy for civilian purposes.
