The breach of the limitation, which restricted Iran’s stockpile of low-enriched uranium to about 660 pounds, does not by itself give the country enough to produce a nuclear weapon. But it signals that Iran may be willing to abandon the limits and restore the far larger stockpile that took the United States and five other nations years to persuade Tehran to send abroad…

While the Trump administration had no immediate reaction to the announcement, Secretary of State Mike Pompeo said last month that the United States would never allow Iran to get within one year of possessing enough fuel to produce a nuclear weapon. His special envoy for Iran, Brian H. Hook, has often said that under a new deal, the United States would insist on “zero enrichment for Iran.”

Iran has so far rejected beginning any negotiation, saying that the United States must first return to the 2015 agreement and comply with all of its terms.