(CNN) -- US President Donald Trump continues to assert that the United States will launch an attack on Iran's Mount Axe site, highlighting a suspected underground nuclear facility where Israel believes Tehran stores part of its enriched uranium stockpile and advanced centrifuge machines.

Trump said Tuesday: "It's very likely that we will hit that area very soon, and they won't be able to do anything about it." In response, Tehran warned that any US attack on Iranian nuclear facilities would be considered an expansion of the war in the region, according to official media early Wednesday.

Here is what we know about the "Mount Axe" site:

What is this site?

Mount Axe is a highly fortified facility deep underground in the center of the country, about a mile south of the Natanz uranium enrichment facility — which has previously been bombed by the United States and Israel — making the site a difficult target for the US and Israel, as well as any potential ground operation.

The facility lies at a depth of at least 100 meters (328 feet) beneath a large mountain called Kuh-e Kolang Ghaz La, where "Kolang" means "axe" in Persian, according to data from the Institute for Science and International Security.

Construction of this facility began in 2020; at that time, Iran informed the UN's International Atomic Energy Agency that the site was intended for future assembly of centrifuges used in nuclear fuel production.

The facility is shrouded in significant mystery; no engineering blueprints are available to the public, and experts primarily draw their conclusions from analysis of satellite imagery. Through these images — as reported in a recent analysis — we know the facility includes multiple tunnel complexes, a wide security perimeter, and concrete-reinforced entrances to protect it from potential airstrikes.

The facility is believed not to be operational yet, as construction is still ongoing. These efforts may have intensified over the past year, with construction accelerating after Israel and the US struck other Iranian nuclear facilities in June 2025; among the sites hit was the Natanz uranium enrichment complex, located just a few miles from Mount Axe.

The Center for Strategic and International Studies noted several possible reasons for this increased activity at the Mount Axe site: Iran may be manufacturing centrifuges, as it previously informed the UN it intended to do; it may be expanding its scope by transferring operations from other destroyed facilities; or it may be building a secret uranium enrichment facility, which is a key element in nuclear weapons production.

Is there enriched uranium there?

An informed Israeli source told CNN that Israeli intelligence believes Iran transferred part of its enriched uranium stockpile and advanced centrifuges to Mount Axe after attacks last June.

During that 12-day war, Israel struck three major Iranian nuclear facilities — Natanz, Isfahan, and Fordow — and killed several senior scientists involved in nuclear research and development programs. The United States joined the fighting near the end of the war, bombing the same three facilities with much more powerful bombs; attacks that President Trump claimed resulted in the "total elimination" of Iran's nuclear capabilities. However, neither the US nor Israel attacked Mount Axe.

Later US and UN intelligence reports indicated that parts of Iran's nuclear program remained intact, albeit damaged. A shared goal for both the US and Israel has been to either force Iran to dispose of its stockpile — about 1,000 pounds — of highly enriched uranium, or seize it from them.

CNN previously reported that Iran had significantly intensified efforts to secure its near-weapons-grade uranium stockpile by deliberately collapsing tunnels and booby-trapping entrances with explosive mines.

When asked whether Iran had moved its advanced centrifuges to the Mount Axe site, Trump seemed to downplay the Israeli reports, saying: "We don't have confirmed information on that."

Earlier in July, a senior security source in Tehran told CNN that claims of nuclear activities at Mount Axe are baseless.

Iran insists its nuclear program is solely for peaceful energy purposes and plans to build additional nuclear power plants to meet domestic energy needs and free up more oil for export.

Could the Mount Axe facility be attacked by the US and Israel?

Analysts' opinions vary. Andrea Stricker, a nonproliferation expert, told CNN that Trump should move to disable the Mount Axe facility to prevent Iran from "reactivating the enrichment option or the nuclear weapons production option, or accessing the thousands of centrifuges that are remnants of its nuclear program."

Although any ground operation would be complex, a report from the Institute for Science and International Security pointed to several possible pathways for an attack.

The report explained that this secret facility requires ventilation, heating, and cooling systems, as well as supply operations, power, and a workforce; all elements that constitute "vulnerabilities that the US and Israel appear capable of exploiting."

However, strikes may not achieve the desired effect, given that the core part of the facility is likely deeply buried underground.

In this context, James Acton — co-director of the Nuclear Policy Program at the Carnegie Endowment — wrote on X that he doubts the US can do more than destroy and collapse the access tunnels to the Mount Axe facility, arguing that such a move "would not fundamentally change the balance of power."