July 23 (Reuters) - U.S. President Donald Trump threatened to attack a site linked to Iran's nuclear program known as Pekax Mountain, a heavily fortified facility deep underground near one of Iran's main nuclear sites.

This threat reflects escalating tensions amid the exchange of strikes between Tehran and Washington in the Gulf, hindering efforts to end the conflict.

Here's what we know about Peaks Mountain:

Where is it located?

Pekax Mountain is located 220 kilometers south of Tehran and two kilometers from the Natanz nuclear complex.

The Natanz site, where two of Iran’s uranium enrichment plants are located, was bombed during the war that began with the United States and Israel on February 28, and during the 12-day war last year.

The Institute for Science and International Security, a U.S.-based think tank focused on nuclear nonproliferation, said the facility, which is still under construction at Peaks Mountain, was not targeted in either of those wars.

The mountain's summit rises to about 1600 meters above sea level.

There were two enrichment facilities operating at Natanz, one above ground and one underground. The UN's International Atomic Energy Agency (IAEA) reported that the above-ground facility was destroyed. The underground facility was likely at least severely damaged.

An Iranian Foreign Ministry spokesman said on July 22 that there was no nuclear activity at Peaks Mountain.

What is Peaks Mountain?

The site is linked to Iran’s nuclear program, which has long strained relations between the West and Iran, which denies seeking to acquire an atomic bomb.

The Institute for Science and International Security said construction of the facility at Pekax Mountain began in 2020 following what Iranian authorities at the time said was an explosion caused by sabotage at the Natanz facility.

Iran stated at the time that the sabotage operation at Natanz caused serious damage that could slow the development of advanced centrifuges for uranium enrichment.

In September of that year, the then-head of Iran’s Atomic Energy Organization, Ali Akbar Salehi, said that Iran had begun building “a more modern, larger, and more comprehensive facility in every respect in the heart of the mountain near Natanz” to manufacture advanced centrifuges.

In a March interview with PBS television, Rafael Grossi, the director general of the UN's International Atomic Energy Agency, noted that Iran had previously announced its intention to conduct nuclear activities at Peaks Mountain.

He added that this falls within what he described as a systematic Iranian trend to move the most important facilities to underground locations.

What did Iran build there?

The Institute for Science and International Security, which analyzed satellite images of the site, says it has four entrances that are presumed to lead to a single facility estimated to be at least 100 meters below the mountain.

The institute stated in a report issued on July 14 that the defensive measures consist mainly of a wide security perimeter and heavy fortifications of the entrances.

The institute's report noted that the two eastern entrances to the tunnel had been partially filled in since last year's war and after the outbreak of the current war to hinder the arrival of land vehicles, but they were not completely closed.

Sam Lear, a researcher at the Foreign Policy Research Institute who also reviewed recent satellite images of the site for Reuters, said that reinforcing the entrances would make it more difficult to "target them with bunker-buster munitions such as bunker-buster bombs."

Is the website operational and what purpose can it be used for?

Trump said in his remarks on July 13 that Washington was closely monitoring Peaks Mountain and had not detected any activity there.

The Institute for Science and International Security stated in its report that its assessment indicates the facility has not yet begun operations, but construction work is ongoing, and it is unclear when it could begin operations based on satellite imagery alone.

He added that if Iran begins to rebuild its centrifuge manufacturing capacity, it may plan to construct a smaller centrifuge assembly facility in Peaks Mountain capable of serving a nuclear weapons program.

How can the site be targeted?

Experts believe the complex, located deep underground, is beyond the range of the most powerful bunker-buster bombs in the US arsenal.

The institute said that targeting the site could be possible through attacks or sabotage carried out by ground forces. It added, "However, there may be vulnerabilities that could be exploited by deep-penetrating weapons via airstrikes."