LAUSANNE, Switzerland -- Iran and six world powers have reached an agreement on "key parameters" of a comprehensive nuclear agreement that must be finalized by June 30, a preliminary deal that U.S. President Barack Obama called "historic" and which was met with celebrations on the streets of Tehran.
EU foreign policy chief Federica Mogherini, reading from a joint statement with Iran at a press conference in Lausanne, Switzerland, said the understanding reached on April 2 is a "decisive step" in the long negotiations to curb Iran's nuclear program in exchange for relief for Tehran from economic sanctions.
She said Iran's uranium-enrichment capacity will be reduced and the Fordow facility will be converted into a nuclear physics research center, among other things, in a future agreement.
She said another aspect of the understanding was that a certain amount of enriched uranium already produced would be taken out of Iran.
Mogherini added that the United States and the EU would lift economic sanctions against Iran only after the United Nations, through the International Atomic Energy Agency, verifies that Iran is meeting its obligations under a comprehensive agreement.
Iranian Foreign Minister Mohammad Javad Zarif said Iran and officials from France, Britain, the United States, Russia, and China, plus Germany -- the so-called P5+1 -- are still "some time away from reaching where we want to be."
He said all UN Security Council resolutions putting sanctions against Iran will be terminated under a comprehensive deal.
But a "fact sheet" issued by U.S. officials said the UN resolutions would be lifted as Iran addresses a list of concerns about its nuclear program.
WATCH: EU foreign policy chief Federica Mogherini announces the deal
News of the deal sparked celebrations in Tehran, with people taking to the streets of the Iranian capital, cheering and honking car horns.
In remarks from the White House, U.S. President Barack Obama called it a "historic" understanding, saying it was a "good deal, a deal that meets our core objectives." He called it "our best option by far," after outlining other military options to prevent Iran from developing a nuclear weapon.
But Obama said our "work is not done" on reaching an Iranian nuclear deal and pledged to "always do what is necessary" to stop Iran from getting a nuclear weapon.
U.S. Secretary of State John Kerry called the understanding reached in Lausanne a "critical milestone" that is a solid foundation for the "good deal we are seeking."
He added that the parameters of a future Iran nuclear deal will make certain that "all pathways to make a nuclear weapon have been cut off."
Kerry said Iran's weapon-grade uranium stockpiles will either be diluted or sold on the international market under terms of a future deal.
British Foreign Secretary Philip Hammond (left), U.S. Secretary of State John Kerry, EU foreign policy chief Federica Mogherini, and Iranian Foreign Minister Muhammad Javad Zarif at the announcement of "key parameters" agreed on a future nuclear deal with Tehran.
British Foreign Secretary Philip Hammond said the preliminary points agreed to are the basis for what could be "a very good deal."
French Foreign Minister Laurent Fabius said there is "still work to do" before a final deal is done.
German Chancellor Angela Merkel said in Berlin that the world has "never been closer" to a deal preventing Iran from producing a nuclear weapon.
Obama later spoke by phone with Israeli Prime Minister Benjamin Netanyahu, who has adamantly warned against any deal that would not do enough to prevent Iran from developing a nuclear weapon.
According to the White House, Obama told Netanyahu that the agreement represents significant progress toward a lasting solution that cuts off all of Iran's pathways to a nuclear weapon.
Obama also said the progress on the nuclear front did not diminish concerns about "Iran's sponsorship of terrorism and threats towards Israel," the White House said.
Netanyahu had been among the most vocal in opposing the international nuclear negotiations with Tehran.
Earlier, Netanyahu demanded in a Twitter post that any deal achieved with Iran "must significantly roll back Iran's nuclear capabilities."
After the preliminary deal was struck, Israel dismissed it as "detached from reality."
In the United States, the speaker of the House of Representatives, John Boehner, said the deal was an "alarming departure" from Obama's original goals and added that Congress must fully review the deal before any sanctions on Iran are lifted.
Obama warned U.S. lawmakers that the United States could be blamed for scuppering a deal if they try to impose new sanctions on Tehran.
The U.S. "fact sheet" said Iran has agreed not to build any new nuclear facilities for the purpose of enriching uranium for 15 years.
The U.S. document added that if Iran fails at any point to fulfill its commitments under an agreement, the U.S. and EU nuclear-related sanctions would "snap back into place." It also said that inspections of Iran's uranium supply chain would last for 25 years after an agreement is signed.
Zarif criticized the U.S. decision to release its own fact sheet on the deal, saying on Twitter: "The solutions are good for all, as they stand. There is no need to spin using 'fact sheets' so early on."
Kelsey Davenport, the director for Nonproliferation Policy at the Arms Control Association in Washington, told RFE/RL the announcement made in Lausanne is a "breakthrough."
She said it "sets out agreements on key parameters that will lead Iran and the P5+1 to craft a strong and effective comprehensive deal that will limit Iran’s nuclear program, put intrusive monitoring on the program, and provide Iran with sanctions relief."
But she added that "a [final] deal is by no means assured, but this is an excellent start."
Iran and the six world powers -- who held talks in the Swiss resort Lausanne for eight days -- missed a March 31 deadline to establish a framework agreement.
Western nations want to ensure Iran cannot build a nuclear bomb, while Tehran wants a swift end to UN, U.S., and European Union sanctions that have badly hurt its economy. Iran maintains its nuclear program is for purely peaceful purposes.
Kerry, Zarif, and other negotiators spent the previous night working on the deal, stopping only at 6 a.m. on April 2.
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Negotiators were wrangling over the scope of uranium enrichment that Iran would be allowed to conduct, where stockpiles of enriched uranium should be stored, proposed limits on Iran's nuclear research and development, and the timing and conditions for the removal of sanctions.
The five permanent UN Security Council nations and Germany are seeking verifiable curbs on Iran’s nuclear program that ensure Tehran is not able to develop nuclear weapons.
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Securing a comprehensive deal after more than two decades of tension over Iran's nuclear program would improve the chances of rapprochement between Iran and the United States, whose relations have been badly strained since the Middle East country's 1979 Islamic Revolution.
But there is no guarantee that the sides will reach agreement on a comprehensive agreement by the self-imposed June 30 deadline.
Conservatives in both the United States and Iran are extremely wary of a deal, as are U.S. allies Israel and Saudi Arabia.
Zarif said that other realms of Iran-U.S. relations had nothing to do with the agreement. "We have serious differences with the United States," he said.
Kerry said the United States remains seriously concerned about Iran's destabilizing activities in the region.
With reporting by Hannah Kaviani of RFE/RL's Radio Farda in Lausanne, RFE/RL's Golnaz Esfandiari in Washington, with AP and Reuters