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

The conflict over the program is about to flare again as President Biden travels next month to Israel and Saudi Arabia, Iran’s two biggest regional rivals.

WASHINGTON — Israeli and American intelligence officials have been watching each day as Iran digs a vast tunnel network just south of the Natanz nuclear production site, in what they believe is Tehran’s biggest effort yet to construct new nuclear facilities so deep in the mountains that they can withstand bunker-busting bombs and cyberattacks.

Though the construction is evident on satellite photographs and has been monitored by groups that track the proliferation of new nuclear facilities, Biden administration officials have never talked about it in public and Israel’s defense minister has mentioned it just once, in a single sentence in a speech last month. In interviews with national security officials in both nations, there clearly were differing interpretations of exactly how the Iranians may intend to use the site, and even how urgent a threat it poses.

But as President Biden prepares for his first trip as president to the Middle East next month — one that will take him to Israel and Saudi Arabia, Iran’s two biggest regional rivals — there is little debate that the conflict over Iran’s nuclear program is about to flare again.

By most accounts, Iran is closer to being able to produce a bomb today than at any other point in the two-decade-long saga of its nuclear program — even if it is planning, as many national security officials believe, to stop just short of producing an actual weapon. On Mr. Biden’s trip, the question of taking more extreme measures to stop Iran, as the United States and Israel have attempted before, will be high on the agenda.

The International Atomic Energy Agency said earlier this month that the country is just weeks away from being able to enrich enough bomb-grade fuel to make a single nuclear bomb — though fashioning that into a usable weapon could take at least another two years, even by the most alarmist Israeli estimates.

Gen. Kenneth F. McKenzie Jr., who retired recently as the head of U.S. Central Command, where he oversaw military planning for dealing with Iran, said Tehran, at least in the short term, was trying to leverage its nuclear capabilities as it negotiates with the United States.

“The Iranians’ highest priority is using the nuclear threat to gain concessions, economic and otherwise,” General McKenzie said.