US President Donald Trump has once again threatened to attack Pickaxe Mountain, a heavily protected underground site in Iran near the country’s damaged Natanz nuclear facility. Trump made the comments on Friday, September 4, saying the United States knows “everybody” moving around the site and could strike it soon. This is not the first time Trump has threatened the location. In July, he also said the US would likely attack Pickaxe Mountain. The latest threat comes as tensions between the United States and Iran remain high. The two countries have exchanged attacks this week, despite US officials giving mixed messages about whether active fighting is continuing. Shortly after Trump’s latest warning, an Iranian oil tanker near Kharg Island was reportedly hit by four US missiles, according to Iranian media. Kharg Island is extremely important to Iran’s economy because it handles most of the country’s oil exports. What is Pickaxe Mountain? Pickaxe Mountain, known in Iran as Kuh-e Kolang Gaz La, is located in Isfahan province, about 220km south of Tehran. It is only around 2km from the Natanz nuclear facility. The site has been dug deep into a mountain and is protected by hundreds of metres of rock. The main underground areas are believed to be at least 100 metres below the surface. Western analysts believe Iran may have planned to use the facility for nuclear-related work. Some have suggested it could eventually be used for uranium enrichment, centrifuge production or other sensitive activities. However, Iran says its nuclear programme is peaceful and is designed for civilian purposes. Why does the site matter? The biggest reason is that Pickaxe Mountain has largely survived previous attacks. Other Iranian nuclear facilities, including parts of Natanz and Fordow, have suffered serious damage from US and Israeli strikes. Pickaxe Mountain, however, remains mostly intact. Experts believe Iran could potentially use the underground tunnels to rebuild parts of its nuclear programme, including centrifuge production or enrichment activities. There have also been reports that Iran may have moved centrifuges into the facility, although the United States has not publicly confirmed those claims. What happened to Iran’s nuclear programme? Iran’s nuclear facilities have suffered major damage during the conflict. Many centrifuges and production sites are believed to have been destroyed. However, the full condition of Iran’s nuclear programme is still unclear. The International Atomic Energy Agency, or IAEA, has said it currently has limited information about Iran’s nuclear materials and their locations. Iran is believed to still have a significant amount of uranium enriched to 60 percent. Uranium needs to be enriched to around 90 percent for weapons-grade material. Iran has denied trying to build nuclear weapons and says its programme is peaceful. For now, Trump’s threat against Pickaxe Mountain has increased fears that another major US-Iran attack could happen, potentially widening the conflict across the region.