Israel has described a framework deal aimed at restricting Iran's nuclear activities as "a step in a very, very dangerous direction."
Iran and six world powers reached an agreement in Switzerland on April 2 on "key parameters" of a comprehensive agreement that the United States said would block "all pathways" for Iran to make a nuclear weapon.
The framework agreement, announced after eight days and nights of tough talks in the Swiss resort city of Lausanne, would place restrictions on Iran's nuclear program in exchange for relief from U.S, European Union, and UN sanctions that have hurt its economy and deepened strains in its ties with the West.
It brings the world to the brink of a solution after more than two decades of tension over Iran's nuclear program, which Tehran says is purely peaceful but which Western governments and Israel fear could be a front for a drive to develop a nuclear bomb.
Iran and the six powers -- the United States, Britain, France, Russia, China, and Germany -- now have three months to iron out details and reach a final agreement by a self-imposed June 30 deadline.
U.S. President Barack Obama, whose legacy will be strongly shaped by success or failure in resolving a standoff that could cause a new Middle East war, called the framework agreement a "historic understanding" that "is a good deal" and "meets our core objectives."
He added that it is "our best option by far" after outlining other ways to try to make sure Iran does not develop a nuclear weapon, including military action.
But Obama said our "work is not done."
WATCH: Obama speaks about the agreement from the White House
But with vocal opposition from Israel and deep concern among Obama's foes in the United States and hard-line conservatives in Iran, its far from guaranteed that a final deal will be forged by June 30.
Israeli government spokesman Mark Regev said on April 3 that Iran's "single goal" behind the accord was to build a nuclear weapon.
"Not only does it leave Iran with an expansive nuclear infrastructure, but it fails to shut down even a single Iranian nuclear installation," Regev said.
News of the framework agreement sparked celebrations in the streets of Tehran.
Iran's ISNA news agency reported that several dozen people enthusiastically greeted Foreign Minister Mohammad Javad Zarif and his team as they left Tehran's Mehr Abad Airport after returning from Lausanne.
The crowd chanted the names of Zarif and Iran's chief nuclear negotiator, Abbas Araqchi.
Iranian President Hassan Rohani said the nuclear understanding reached between six world powers and Iran will be a "historic memory" for the Iranian people.
Speaking in a nationally televised address, he said Iran believed that in today's world, "threatening and pressuring others" does not work and any agreement should be a "win-win deal" for all sides.
Rohani added that it now depended on "both sides keeping promises" to put the final touches on the agreement.
Delivering the weekly sermon at Tehran University on April 3, Ayatollah Mohammad Emami-Kashani described the Iranian negotiating team as "firm, wise, and calm," the ISNA news agency reported.
He said Supreme Leader Ayatollah Ali Khamenei "supports these representatives," suggesting Khamenei supports the preliminary accord.
"We really have to say congratulations and well done" to President Hassan Rohani and Zarif, Emami-Kashani added.
Earlier, Hossein Shariatmadari, an adviser to Khamenei and editor of the Kayhan daily, said Iran replaced its "ready-to-race horse with a broken bridle," suggesting the deal was bad for Iran and would cripple its nuclear program.
Speaking at a news conference in Tehran on April 3, Zarif said Iran’s nuclear program "will continue."
“None of our facilities will be closed down," he added.
Earlier in Lausanne, Zarif said Tehran and the global powers were still "some time away from reaching where we want to be."
Iranian Foreign Minister Mohammad Javad Zarif said the sides are still "some time away from reaching where we want to be."
U.S. Secretary of State John Kerry, who spent hours in talks with Zarif both in Lausanne and during months of negotiations following the conclusion of a preliminary deal in November 2013, called the understanding a "critical milestone" that is a solid foundation for the "good deal we are seeking."
He said the deal, if finalized and implemented, would 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.
U.S. Secretary of State John Kerry called the understanding a "critical milestone."
France's Foreign Minister Laurent Fabius said on French radio that the framework agreement was a "very important" step, adding that "the end of the road is the end of June."
In Kyrgyzstan’s capital, Bishkek, Russian Foreign Minister Sergei Lavrov praised the framework agreement as "encouraging."
Russia's Foreign Ministry said resolving the dispute over Iran's nuclear program would improve security in the Middle East and allow Tehran to "take more active part in resolving a whole series of issues and conflicts in the region."
But Russia's chief negotiator at the talks, Deputy Foreign Minister Sergei Ryabkov, called for the swift removal of sanctions. He said that EU and U.S. sanctions against Iran were unlawful and should be "lifted immediately, as soon as possible."
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In the United States, House Speaker 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 tried to impose new sanctions on Tehran.
With reporting by Golnaz Esfandiari in Washington, Hannah Kaviani of RFE/RL's Radio Farda in Lausanne, RFE/RL's Tajik Service, AP, Reuters, AFP, and dpa