(CNN) -- Geneva, Switzerland (CNN) -- [Breaking news update, 10:32 p.m. ET]
-- The White House said that "the initial, six-month" Iran nuclear deal addresses the United States' "most urgent concerns." Among them are Iran's ability to enrich uranium, what to do about its existing enriched uranium stockpiles, the number and potential of its centrifuges and Tehran's "ability to produce weapons-grade plutonium using the Arak reactor." Iran also agreed to provide "increased transparency and intrusive monitoring of its nuclear program."
-- "We think we have a good strong arrangement," U.S. Secretary of State John Kerry told CNN following the announcement of a nuclear deal with Iran.
[Original story published at 10:23 p.m. ET]
EU spokesman: Iran nuclear deal reached
A historic deal was struck early Sunday between Iran and six world powers over Tehran's nuclear program, a first step in ending a decades-long standoff over the country's nuclear intentions.
The agreement was expected to be signed within hours, capping days of marathon talks in which diplomats worked to overcome issues surrounding the wording of an initial agreement that reportedly would temporarily freeze Iran's nuclear development program and lift some sanctions while a more formal deal is worked out.
"At three o'clock in the morning on the fifth day, white smoke in the negotiations!" Iran Deputy Foreign Minister Seyed Abbas Araghchi said in a post on Twitter.
The spokesman for the European Union, Michael Mann, also took to Twitter to tout the success: "We have reached agreement."
Catherine Ashton, the EU's foreign policy chief, formally announced the agreement in Geneva where the foreign ministers representing Iran, the United States, Britain, China, Russia, France and Germany were meeting.
The Iran nuclear deal is a first step requiring actions by both sides, which have "a strong commitment to negotiate a final comprehensive solution," Ashton said.
According to a senior U.S. administration official, speaking on condition of anonymity, the deal halts Tehran's nuclear program, including halting the development at the Arak reactor and requiring all of the uranium enriched to 20 percent -- close to weapons-grade -- to be diluted so it cannot be converted for military purposes.
But there were conflicting reports about whether Iran's right to enrich uranium had been recognized.
The senior administration official said the deal does not recognize the right, while Iranian Deputy Foreign Minister Seyed Abbas Araghchi -- on a Twitter feed commonly attributed to him by Iranian media -- said that "our enrichment program was recognized."
"Congratulation to my nation which stood tall and resisted for the last 10 years," Araghchi said in the post.
For years, Iran and Western powers have left negotiating tables in disagreement, frustration and at times open animosity.
But the diplomatic tone changed with the transfer of power after Iran's election this year, which saw President Hassan Rouhani replace Mahmoud Ahmadinejad.
Caustic jabs at the United States and bellicose threats toward Israel were a hallmark of Ahmadinejad's foreign policy rhetoric.
He lambasted the West over the economic sanctions crippling Iran's economy and at the same time, pushed the advancement of nuclear technology in Iran.
Rouhani has struck up a more conciliatory tone and made the lifting sanctions against his country a priority.
Despite the sanctions, Iran today has 19,000 centrifuges and is building more advanced ones, according to Mark Hibbs, a nuclear policy expert at the Carnegie Endowment for International Peace.
Most world powers believe that Iran could not realistically build a usable bomb in less than a year, Hibbs said.
And Iran recently signed a deal with the International Atomic Energy Agency that agrees to give the U.N. nuclear watchdog agency access to long-unseen nuclear sites, including a heavy-water reactor in Arak.
Tehran is also a party to the Treaty on the Non-Proliferation of Nuclear Weapons, which requires it not to create nuclear weapons or enable other countries to obtain them.