WASHINGTON — Iran said on Sunday that it will breach the terms of the nuclear deal it signed with the U.S. and other powers, vowing to enrich uranium beyond the cap set by the 2015 agreement.

The enrichment work would break the limits of the deal later on Sunday and the government planned an additional unspecified step within 60 days that would breach other provisions in the agreement, Iran’s deputy foreign minister, Abbas Araghchi, told a news conference in Tehran. But he said Iran remains open to diplomacy and still believes the nuclear agreement is valid.

European governments said they are "extremely concerned" by the move and urged Tehran to reconsider. But just how significant is Iran's announcement and how much closer could Tehran be to having the capability to build a nuclear weapon?

Iran has said repeatedly it is not building a bomb and the country's supreme leader, Ali Khamenei, has stated the same in speeches and religious edicts for more than a decade, saying nuclear weapons are forbidden under Islam. Iranian Foreign Minister Javad Zarif cited the supreme leader's fatwa in a tweet in May. A U.S. National Intelligence Estimate made public in 2007 concluded that Iran "halted its nuclear weapons program" in 2003.

While Iran is moving gradually beyond the limits of the JCPOA, the international deal from which the U.S. withdrew in 2018, it is still some distance from being able to build a nuclear device. If Tehran were to opt to move down that path, it could take months or possibly more than a year, experts and former government officials said, and U.N. inspectors would be able to detect any violation of the deal at every stage.

Ayatollah @khamenei_ir long ago said we're not seeking nuclear weapons—by issuing a fatwa (edict) banning them.#B_Team's #EconomicTerrorism is hurting the Iranian people & causing tension in the region. Actions—not words—will show whether or not that's @realDonaldTrump's intent — Javad Zarif (@JZarif) May 27, 2019

"This is not a sprint to a bomb," said Mary Kaszynski, deputy director of policy at the Ploughshares Fund, a non-profit that supports the nuclear agreement. "This is a message, not a threat."

Iran is breaching the deal in small steps to try to signal to the Europeans the need for some economic relief from U.S. sanctions, and to push the Trump administration to back off of its "maximum pressure" campaign, she and other experts said.

Uranium enrichment and the nuclear deal

The 2015 nuclear agreement between Iran and the U.S., Britain, France, Germany, Russia and China required Tehran to accept strict limits on its nuclear program in return for a lifting of a range of economic sanctions. President Donald Trump pulled the U.S. out of the deal in May 2018.

The deal bars Iran from enriching uranium beyond 3.67 percent, the level needed to run a nuclear power reactor. A higher level of enrichment is needed for research reactors, about 12 to 19.75 percent.

Nuclear weapons usually require uranium enriched to 90 percent. Moving from three percent to 20 percent presents a major technical challenge, but once that hurdle is overcome, it is a relatively quick step to go from 20 percent to weapons-grade, experts say.

Iranian President Hassan Rouhani said that starting Sunday, his government would no longer abide by the limit on the enrichment level, saying the enrichment rate will be "as much as we want it to be."

Ali Akbar Velayati, an adviser to the supreme leader, also said Iran planned to increase enrichment without specifying at what rate, but he mentioned a level of 5 percent he said was needed to produce electricity at the country’s Bushehr nuclear power plant.

Western governments and arms control experts view anything above 20 percent enrichment as an alarming step toward the highly enriched uranium needed for a nuclear weapon.

Before the nuclear deal was negotiated, the U.S. and European governments sought to impose punitive sanctions on Iran after Tehran began enriching uranium to a 20 percent level in 2010.

Uranium ore — U238 — is a common metal. It contains less than one percent — about 0.7 percent — of U235, the fissile material needed for an atomic bomb. Enrichment is carried out by separating U235 from U238 using centrifuges, electromagnetics, lasers or chemical reactions. Centrifuges are the most efficient method and the one used by other countries to develop nuclear weapons.

It could take up to a year or more for Iran to produce enough highly enriched uranium for a weapon, experts said. That timeline could be shortened if Iran chose to violate the agreement's limits on the number and quality of its centrifuges. (The JCPOA forced Iran to give up two-thirds of its centrifuges.) But U.N. inspectors, who have access to nuclear sites under the 2015 deal, would almost certainly spot any attempt to expand the country's supply of centrifuges.

Before the 2015 deal was clinched, experts estimated Iran was up to three months away from having enough fissile material for an atomic bomb. Under the agreement, Western governments say Iran is about a year away.

Stockpiles of uranium

The deal also restricted Iran from holding a stockpile of more than 300 kilograms of low enriched uranium. Iran announced on Monday, and the International Atomic Energy Agency confirmed, that it has exceeded the limit on the stockpile.

It would take a much larger amount, about 1,500 kilograms of 3.67 percent enriched uranium, to make the core of one nuclear weapon. Then the uranium would need to be further enriched to a 90 percent level.

Before signing the 2015 nuclear deal, Iran had more than 10,000 kilograms of low-enriched uranium. But the government was required to ship 98 percent of the material out of the country.

The move to surpass the stockpile cap represents a less dramatic breach than Iran's plans to violate the limits on uranium enrichment, experts said. Both steps combined, however, open up a potential path to a nuclear weapon for Iran, and could shrink the one-year timeline to secure a sufficient amount of weapons-grade uranium.

Iran's Foreign Minister Zarif says his country has not violated the deal by exceeding the limit on stockpiles, citing provisions in the accord that allow Tehran to cease carrying out the accord if other parties do not uphold their end of the bargain. Zarif tweeted that Iran would be ready reverse course if European governments "abide by their obligations" under the deal.

After producing enough weapons-grade uranium for a bomb, Iran would then need to convert the uranium from gas to metal. After that, it would need to shape and miniaturize the material to mount it on a ballistic missile. That task could take anywhere from a few months to a year, experts say.

Bombs and politics

Both opponents and supporters of the nuclear deal agree that Iran's decision to begin breaching elements of the agreement is less about trying to build a bomb and more about political tactics.

Iran is positioning itself for any future negotiations with the United States, said Behnam Ben Taleblu. a senior fellow at the Foundation for Defense of Democracies, a think tank that has sharply criticized the nuclear deal.

"This is a way for Iran to build up its leverage," he said. "It carries a political message. The message is to get the maximum pressure diluted."

But it's not clear if the Iranian tactic will work. If Tehran violates additional provisions of the agreement, European governments will eventually have to reimpose their sanctions on Iran, as the deal requires, foreign diplomats say.

In the meantime, tensions are rising and neither the U.S. nor Iran appears ready to enter into negotiations.

In a commentary on Tuesday, the former French ambassador to the U.S., Gerard Araud, urged the two sides to sit down for talks without preconditions, or else risk a "catastrophic conflict, the costs of which would be hard to fathom and the consequences of which will haunt the world for years to come."