Iran Nears an Atomic Milestone

“I’m not going to put a date on it,” he told reporters, “but we are getting closer to the point at which a strict return to compliance” with the old deal “does not reproduce the benefits that agreement achieved.”

He said that “as time goes on and as Iran continues to make advances in its nuclear program, including spinning more sophisticated centrifuges, enriching more material, learning more, there is a point at which it would be very difficult to regain all of the benefits” of the restrictions Iran agreed to six years ago. “We’re not at that point yet, but it’s getting closer,” he added.

The next few weeks are regarded as critical. The opening of the United Nations General Assembly is traditionally a moment for back-room diplomacy, especially on Iran, and officials of the new Iranian government, including the new foreign minister, Hossein Amir Abdollahian, are expected to make debut appearances. Considered a hard-liner, the 56-year-old Mr. Amir Abdollahian has indicated a willingness to renew the agreement — but on terms that the new government can say are vastly improved.

Outside experts say that both Iran and North Korea, which fired a new cruise missile on Sunday that demonstrated an ability to avoid missile defenses, see this as a moment to test the Biden administration.

“There’s an eerie similarity between what we’re seeing in Iran with enrichment and in North Korea with the cruise missile test,” said Rose Gottemoeller, a former arms control official in several administrations who now works at Stanford University. “They’re both trying to set the negotiating table in their favor as the Biden administration finally turns to them.”

On Sunday, Iranian officials reached a temporary agreement with the director-general of the International Atomic Energy Agency, Rafael M. Grossi, to let the agency reset monitoring devices that help measure the progress of the country’s nuclear program. In recent months, agency inspectors have been blinded in their efforts to monitor some facilities, a growing source of concern to American officials, who fear that nuclear material could be diverted.

The accord heads off an immediate inspection crisis, assuming the inspectors are allowed to gain access to their cameras and other equipment and get them operating again. But it does not address the country’s drive to restore its uranium production — and to enrich at levels far higher, and thus far closer to bomb-grade material, than it did before 2015.