Over the past 20 months, Israeli intelligence operatives have assassinated Iran’s chief nuclear scientist and triggered major explosions at four Iranian nuclear and missile facilities, hoping to cripple the centrifuges that produce nuclear fuel and delay the day when Tehran’s new government might be able to build a bomb.

But American intelligence officials and international inspectors say the Iranians have quickly gotten the facilities back online — often installing newer machines that can enrich uranium at a far more rapid pace. When a plant that made key centrifuge parts suffered what looked like a crippling explosion in late spring — destroying much of the parts inventory and the cameras and sensors installed by international inspectors — production resumed by late summer.

One senior American official wryly called it Tehran’s Build Back Better plan.

That punch and counterpunch are only part of the escalation in recent months between Iran and the West, a confrontation that is about to come to a head, once again, in Vienna. For the first time since President Ebrahim Raisi took office this summer, Iranian negotiators plan to meet with their European, Chinese and Russian counterparts at the end of the month to discuss the future of the 2015 nuclear agreement that sharply limited Iran’s activities.

American officials have warned their Israeli counterparts that the repeated attacks on Iranian nuclear facilities may be tactically satisfying, but they are ultimately counterproductive, according to several officials familiar with the behind-the-scenes discussions. Israeli officials have said they have no intention of letting up, waving away warnings that they may only be encouraging a sped-up rebuilding of the program — one of many areas in which the United States and Israel disagree on the benefits of using diplomacy rather than force.

At the Vienna meeting, American officials will be in the city but not inside the room — because Iran will not meet with them after President Donald J. Trump pulled out of the accord more than three years ago, leaving the deal in tatters. While five months ago those officials seemed optimistic that the 2015 deal was about to be restored, with the text largely agreed upon, they return to Vienna far more pessimistic than when they last left it, in mid-June. Today that text looks dead, and President Biden’s vision of re-entering the agreement in his first year, then building something “longer and stronger,” appears all but gone.

It is a sign of the changed mood that Ali Bagheri Kani, Iran’s newly appointed chief nuclear negotiator, does not refer to the upcoming talks as nuclear negotiations at all. Mr. Bagheri Kani, a deputy foreign minister, said in Paris last week that “we have no such thing as nuclear negotiations.” Instead, he refers to them as “negotiations to remove unlawful and inhuman sanctions.” Iran says it will insist on the lifting of both nuclear and non-nuclear sanctions, and that it needs a guarantee that no future president could unilaterally abandon the agreement, as Mr. Trump did. Biden administration officials say the president would never make such a commitment.

Iran, as always, denies that it has any intention of ever building a nuclear weapon. But the more likely scenario is that it wants a “threshold capability” — one that would leave it able to produce a weapon in weeks or months, if it felt the need.

Publicly, the United States is hinting that if Iran stonewalls in Vienna, it may have to consider new sanctions.

He noted that Mr. Biden and Secretary of State Antony J. Blinken “have both said if diplomacy fails, we have other tools — and we will use other tools to prevent Iran from acquiring a nuclear weapon.”

But inside the White House, there has been a scramble in recent days to explore whether some kind of interim deal might be possible to freeze Iran’s production of more enriched uranium and its conversion of that fuel to metallic form — a necessary step in fabricating a warhead. In return, the United States might ease a limited number of sanctions. That would not solve the problem. But it might buy time for negotiations, while holding off Israeli threats to bomb Iranian facilities.

Buying time, perhaps lots of it, may prove essential. Many of Mr. Biden’s advisers are doubtful that introducing new sanctions on Iran’s leadership, its military or its oil trade — atop the 1,500 Mr. Trump imposed — would be any more successful than past efforts to pressure Iran to change course.

And more aggressive steps that were successful years ago may not yield the kind of results they have in mind. Inside the National Security Agency and U.S. Cyber Command, there is consensus that it is much harder now to pull off the kind of cyberattack that the United States and Israel conducted more than a decade ago, when a secret operation, code-named “Olympic Games,” crippled centrifuges at the Natanz nuclear enrichment site for more than a year.

Current and former American and Israeli officials note that the Iranians have since improved their defenses and built their own cyberforces, which the administration warned last week were increasingly active inside the United States.

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The Iranians have also continued to bar inspectors from key sites, despite a series of agreements with Rafael M. Grossi, the head of the International Atomic Energy Agency, the United Nations’ watchdog, to preserve data from the agency’s sensors at key locations. The inspectors’ cameras and sensors that were destroyed in the plant explosion in late spring have not been replaced.