The United States, Iran and five other world powers say they have reached an understanding that will lead to a comprehensive nuclear agreement within three months.
Reading out a joint statement on Thursday evening, EU foreign policy chief Federica Mogherini said a "decisive step" has been achieved.
The agreement, announced in the Swiss city of Lausanne on Thursday, will curb Iran's nuclear capacities by reducing its enrichment capacity and end most sanctions imposed on the country because of its programme.

Foreign Minister Javad Zarif welcomed the agreement as he read out the same statement in the news conference. He described the deal as a "win-win" agreement.
US President Barack Obama said the US and its allies had "reached a historic understanding with Iran, which if implemented will prevent Iran from obtaining a nuclear weapon."
Obama said the deal was a "long time coming" and added it would not be based on trust but on independent verification of Iran's commitments.

'Solid foundation'
US Secretary of State John Kerry said the agreement in Lausanne was a "solid foundation for a good deal".
Al Jazeera's James Bays, reporting from Lausanne, said that US diplomats still faced the challenge of convincing opposition Republican dissenters in Congress, and its strongest ally, Israel, that the deal was sufficient.

"There are a lot of places where this deal will not be accepted and one of those is Israel," Bays said.
Obama said his security officials would be working with Israel and Arab states, including Saudi Arabia, to make sure their concerns are addressed.
The deal will limit Iran's nuclear activity to the Natanz plant and reduce the number of centrifuges it operates from 19,000 today to just over 6,104.
Iran has also agreed to not build any new facilities for the purpose of enriching uranium for 15 years.
Zarif said the countries had agreed an elaborate mechanism if any of the parties to the agreement "returned to old practices" and reneged on their obligations.

"We will not allow excuses that will allow a return to the old system," Zarif said.
Mogherini said the seven nations would now start writing the text of a final accord.
She cited several agreed-upon restrictions on Iran's enrichment of material that can be used either for energy production or in nuclear warheads. She said Iran will not produce weapons-grade plutonium.
Phased approach
Iran's commitments on limiting domestic enrichment capacity will last ten years, with additional aspects of its programme, such as limitations on the amount of enriched uranium stockpiles it can hold, will last 15 years.

The lifting of sanctions placed on Iran will follow verification by the Un nuclear watchdog, IAEA, that it has met the obligations placed on it in the agreement.
The US, Britain, France, Germany, Russia and China have negotiated with Tehran for years to prevent it from acquiring the means to develop a nuclear bomb.
Tehran had insisted on the lifting of international sanctions that have crippled its economy, while preserving what it views as its right to nuclear technology for peaceful purposes.
Source: Al Jazeera and agencies