Fears Grow Over Iran’s Nuclear Program as Tehran Digs a New Tunnel Network

The deal, which President Donald J. Trump abandoned in 2018, limited Tehran’s ability to install new centrifuges and forced it to ship 97 percent of its nuclear fuel out of the country. Mr. Biden’s refusal of Iran’s demand to remove the Islamic Revolutionary Guards Corps from the list of terrorist organizations, along with a flow of new revenue to Tehran resulting from today’s soaring oil prices, have contributed to the stalemate in the talks.

Now, the Iranians are looking for new pressure points, including the excavation of the mountain plant near Natanz. And over the past week, Iranian authorities have switched off 27 cameras that gave inspectors a view into Iran’s production of fuel.

The decision to cut off the cameras, which were installed as part of the nuclear deal, was particularly worrisome to Rafael Grossi, the director general of the International Atomic Energy Agency, the United Nations agency responsible for nuclear inspections. If the cameras remain off for weeks, and it is impossible to track the whereabouts of nuclear materials, “I think this would be a fatal blow” to hopes of reviving the accord, Mr. Grossi said last week.

But this is far more than an inspection dispute. In the eyes of experts, Tehran is getting to the point of becoming what Robert Litwak, who has written extensively on the Iranian program at the Woodrow Wilson International Center for Scholars in Washington, called a “nuclear threshold state whose uranium enrichment program creates an inherent option — a hedge — to produce nuclear weapons,” without actually taking the last step.

“Iran’s move at Natanz,” he said of the plant now under construction, “amps up pressure on the United States to reach a new deal by highlighting the risk of a nuclear breakout should diplomacy fail.”

For decades, a barren piece of land near Natanz has been the centerpiece of Iran’s nuclear effort. The country has always maintained that its underground “pilot plant” there is working only to produce nuclear fuel for peaceful purposes — the production of nuclear energy. The evidence, some of it stolen by Israel from a warehouse in Tehran, suggests otherwise: that Iran has had plans in place for two decades to construct a bomb, if it concludes that it was in its interest.