Explainer-What is Pickaxe Mountain, the Iranian nuclear-linked site threatened by Trump?

July 15 - U.S. President Donald Trump has threatened to attack a site linked to Iran's nuclear programme known as Pickaxe Mountain, a fortified facility buried deep underground near one of Tehran's main nuclear sites.

"We're going to take out Pickaxe Mountain. Tell the Iranians to be ready," Trump said in a July 13 interview on the Hugh Hewitt Show.

The threat reflects escalating tensions as Tehran and Washington trade fire in the Gulf, setting back efforts to end the conflict.

Here's what we know about Pickaxe Mountain:

WHERE IS IT?

Pickaxe Mountain is located 220 km (140 miles) south of Tehran and 2 km (1.2 miles) from the Natanz nuclear complex.

The Natanz site, where two of Iran's uranium enrichment plants were located, was bombed during the war started by the United States and Israel on February 28, and during last year's 12-day war.

The tunnel facility under construction at Pickaxe Mountain wasn't targeted in either of those wars, according to the Institute for Science and International Security (ISIS), a U.S.-based think-tank focused on nuclear non-proliferation.

The peak rises to some 1,600 metres above sea level.

There were two enrichment plants in operation at Natanz - one above and one below ground. The U.N. nuclear watchdog has said the above-ground one was destroyed. The other, underground one was likely at least badly damaged.

WHAT'S THE HISTORY OF THE SITE?

The site is linked to Iran's nuclear programme, which has long caused tension between the West and Iran, which denies seeking an atomic bomb.

Construction of the facility at Pickaxe Mountain began in 2020, according to ISIS, following what Iranian authorities reported at the time as an explosion caused by an act of sabotage at the Natanz facility.

Iran said at the time the Natanz sabotage had caused significant damage that could slow the development of advanced uranium enrichment centrifuges.

In September that year, Iran's then-nuclear chief,  Ali Akbar Salehi, said Iran had started building "a more modern, larger and more comprehensive hall in all dimensions in the heart of the mountain near Natanz" for making advanced centrifuges.

Rafael Grossi, the chief of the U.N. nuclear watchdog, in an interview with PBS Frontline in March, noted that Iran had previously announced its intention to have nuclear activity at Pickaxe Mountain.

"This was part of their quite systematic intention to put their most sensitive facilities underground," he said.

WHAT HAS IRAN BUILT THERE?

ISIS, which has analyzed satellite imagery of the site, says it features two pairs of entrances, which are assumed to lead to one facility estimated to be at least 100 metres under the mountain.

The physical defensive measures consist primarily of a large security perimeter and the extensive hardening of tunnel entrances, ISIS said in a July 14 report.

The pair of eastern tunnel portal entrances have been partially backfilled since the wars to obstruct ground vehicle access but they have not been sealed fully, the ISIS report said.

Sam Lair, a fellow at the Foreign Policy Research Institute, who also reviewed recent satellite imagery of the site, told Reuters that increasing the strength of the tunnel entrances would complicate "targeting with penetrating munitions like bunker busters".

IS THE SITE FUNCTIONING AND WHAT COULD IT BE USED FOR?

Trump, in his July 13 remarks, said Washington was watching Pickaxe Mountain closely.

"We see no activity there. They're not doing well with their nuclear situation. Every time we hear about it, we blow it up. So they don't like talking about it. But we'll probably give Pickaxe a shot relatively soon," he said.

ISIS, in its report, said its assessment "is that the facility is not yet operational, but construction continues", and that it was unclear when it could be operational, based on satellite imagery alone.

"It is also unclear if Iran still plans on installing a large-scale assembly facility, given the destruction of Iran’s centrifuge program, including Iran’s ability to make centrifuge components needed for an assembly plant.

"Nonetheless, if Iran starts to rebuild its centrifuge manufacturing capability, it could plan to install a smaller centrifuge assembly facility in Pickaxe Mountain able to serve a nuclear weapons program," ISIS said.

HOW MIGHT THE SITE BE ATTACKED?

Experts assess the deeply buried complex is beyond the reach of the most powerful bunker buster bombs in the U.S. arsenal.

ISIS said the site "would be more suitable for ground forces to attack or sabotage".

"However, vulnerabilities may also exist that can be exploited by deep earth penetrating weapons via aerial attacks," it said.

Lair said: “We can infer that there are ongoing activities at Pickaxe Mountain the Iranians wish to continue but are still concerned enough about a potential attack that they are taking steps to bolster their defenses.” REUTERS