Iran is believed to have moved thousands of its uranium-enrichment centrifuges into the tunnels deep inside the Pickaxe Mountain site last year, according to Israeli intelligence sources.

The site, located in the mountains about one mile south of the Iranian nuclear complex at Natanz, was used to conceal the centrifuges after "Operation Midnight Hammer" and the Twelve-Day War, the Israeli sources told the United States, The Wall Street Journal reported Tuesday.

President Donald Trump said after the attacks last summer that Iran's nuclear capabilities at the Fordow Uranium Enrichment Plant, the Natanz Nuclear Facility, and the Isfahan Nuclear Technology Center were "obliterated."

Trump said earlier this month that the United States is prepared to attack Pickaxe Mountain, while Israeli Prime Minister Benjamin Netanyahu has called for broader attacks on Iran to push back against its weapons programs.

Trump told conservative broadcaster Hugh Hewitt that Pickaxe is a "possible target for a nice big fat shot."

He had not previously identified the mountain as a target, but he has mentioned an Iranian underground facility buried in granite.

Pickaxe is known as Mount Kolang in Iran and has been under U.S. and Israeli surveillance.

The site was commissioned to replace an Iranian centrifuge-assembly location that was damaged in a 2020 explosion, widely believed to have been the result of sabotage.

The complex is estimated to extend 300 to 450 feet beneath solid rock and has enough room for several nuclear facilities.

Iran has denied seeking nuclear weapons. Still, it has produced about 1,000 pounds of uranium enriched to 60%, bringing it closer to weapons-grade material.

It is not clear where the centrifuges Israel claims were taken to Pickaxe came from, but spare machines could have been at Iran's main nuclear sites.

Meanwhile, Iran has not given the International Atomic Energy Agency access to Pickaxe or provided the agency with information about its plans or work at the site.

IAEA Director General Rafael Grossi said in March that Iran announced in 2021 that it had the "intention to have nuclear activity" at Pickaxe.

According to the Institute for Science and International Security, a think tank that examines nonproliferation and nuclear matters, activity has continued at Pickaxe for the past 15 months, including a security perimeter and reinforced tunnels.

Work has also been carried out around an older tunnel network. The network dates to 2007, and Iran has since sealed it.

Institute President David Albright conceded that "it is plausible that Iran moved centrifuges" into the Pickaxe tunnels.

Nate Swanson, who served as a U.S. National Security Council director for Iran during the Biden administration, agreed that Tehran's covert nuclear history means that any activity going on in an underground site like Pickaxe is a reason to be concerned.

"A covert breakout is the worst-case scenario," he told The Wall Street Journal. "We don't know what Iran's intentions are, but the fact that we can't verify this site underscores how problematic the status quo is. We have to have the IAEA in there to inspect these things."

Pickaxe has not yet been targeted in the current conflict with Iran, which began on Feb. 28.

However, an Israeli military official familiar with the targeting efforts said he was concerned that the airstrikes had not targeted Iran's nuclear weapons-related work.