Iran is building up defenses in an underground complex near its nuclear facility, say experts analyzing new satellite photos. The site at Pickaxe Mountain has tunnel entrances being reinforced with fresh concrete, according to the Institute for Science and International Security (ISIS). Experts believe this could protect uranium enrichment activities or key equipment. The exact purpose is unclear. Iran denies any weapon ambitions, but US President Donald Trump has warned that Iran is close to nuclear weapons and threatened strikes if no deal is reached. The nearby Natanz nuclear site, hit by US and Israeli air strikes last year, is also undergoing repairs and new defenses. Similar work is happening at the Isfahan nuclear complex, where tunnels are now sealed with earth to protect against air or ground attacks. A new roof also covers a repaired building used for centrifuge manufacturing, damaged in past strikes. Prof Sina Azodi says Iran is preparing for future attacks and can rebuild its nuclear program despite hits. Meanwhile, the International Atomic Energy Agency’s head Rafael Grossi urges swift action to make a new nuclear deal possible before the chance closes. He confirms Iran’s enriched uranium remains underground despite US strikes last year.