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. 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, with a boom pump visible at the location. Analysts from both ISIS and UK-based intelligence analysis firm Maiar agree that recent changes indicate Iran is bolstering defenses against potential airstrikes, although the ongoing presence of construction materials suggests the facility may not be operational yet. Recent satellite images also show work at the Natanz nuclear site and Isfahan nuclear complex to seal entrances, which ISIS states would help protect against air strikes. Rafael Grossi, the head of the International Atomic Energy Agency, noted a necessity for a new nuclear deal and signaled that while Iran's nuclear program is not destroyed, it poses a continuous concern.