Iran fortifies underground complex near nuclear site, satellite images show

Iran has been fortifying an underground complex near one of its nuclear facilities, according to analysis of new satellite images.

This activity comes at a time of heightened tensions as talks between Iranian and US officials continue, with President Donald Trump threatening fresh military action against Iran if it does not agree a new deal on its nuclear programme.

The photos, first analysed by the Institute for Science and International Security (ISIS), a US-based think tank, show tunnel entrances being strengthened at Mount Kolang Gaz La - also known as Pickaxe Mountain.

Experts say this facility may be designed to protect Iran's uranium enrichment activities or key equipment, but its exact purpose - and whether it is operational - remains unclear.

Iran insists its nuclear programme is entirely peaceful and denies it is seeking to develop nuclear weapons.

However, Trump said Iran was as little as a month away from having a nuclear weapon in June 2025, when he ordered strikes on three underground nuclear sites where centrifuges were being used to produce highly enriched uranium during a 12-day war between Israel and Iran last year.

Trump said the strikes had "obliterated" Iran's enrichment capacity, but that Iranian officials "were thinking about starting a new site".

Pickaxe Mountain was not one of the locations attacked in US and Israeli air strikes in June 2025, but the Natanz nuclear facility, located about 2km (1.24 miles) north, was hit.

A satellite image from 10 February shows what appears to be fresh concrete laid on top of one of the Pickaxe Mountain entrance areas.

A boom pump used to deliver concrete can be seen at the location, analysts from both ISIS and UK-based intelligence analysis firm Maiar agreed.

At another tunnel entrance, rock and soil has been pushed back and flattened. There's also a new concrete-reinforced structure nearby.

Experts at ISIS suggest these changes are intended to strengthen the tunnel entrances and give additional protection against a potential air strike.

ISIS says the ongoing presence of heavy construction machinery and material indicates the facility is not likely to be ready for operations yet.

"In the past, Iran has tied the construction to rebuilding an advanced centrifuge assembly plant, but the size of the facility, as well as the protection provided by the tall mountain, raised immediate concern whether additional sensitive activities are planned, such as uranium enrichment," they said.

Satellite images also show repair work and defensive strengthening has been taking place at the nearby Natanz nuclear site and at the Isfahan nuclear complex, 125km (77 miles) to the north, in recent weeks.

At Isfahan, all entrances to its tunnel complex now appear to be sealed off with earth, satellite images reviewed by ISIS reveal.

Backfilling the tunnel entrances like this would "help dampen" any air strike, ISIS says, as well as help to defend against a land-based assault to seize or destroy any highly enriched uranium that may be housed inside.

ISIS has assessed the roof was added to block the view of anyone trying to observe what Iran was doing beneath it.

Prof Sina Azodi, director of the Middle East Studies Program at George Washington University in the US, says Iran is "operating under the assumption that the attacks are going to happen and they need to protect the facilities as much as they can".

"[The] Iranian nuclear programme hasn't been destroyed," he added. "Clearly once you have the knowledge and capacity and technology to reconstruct the programme, you can always rebuild everything."

Rafael Grossi, the head of the global nuclear watchdog, the International Atomic Energy Agency, told the BBC a new nuclear deal between Iran and the US was possible and was urgently needed.

"My sense, talking to all those involved, is that we have a window of opportunity, but windows of opportunity have a tendency to shut themselves quite abruptly and brusquely, so I think the we need to seize the moment," he said in an interview at the Munich Security Conference.

He also said he believed Iran's estimated 400kg of highly enriched uranium - which is a short, technical step away from weapons grade - remained in the underground tunnels and chambers where the US dropped bunker-busting bombs last June.