The International Atomic Energy Agency (IAEA) has detected construction activity at Iran's heavily fortified Pickaxe Mountain facility, IAEA Director General Rafael Mariano Grossi said on Thursday.
Speaking to Bloomberg TV, Grossi said that while IAEA inspectors have not entered the tunnel complex, remote imagery has shown indications of movement around the site.
“There are some indications that there is movement around this construction site," Grossi said, adding that the agency does not have concrete information regarding what activities may be underway there.
Grossi's comments came after the IAEA's Board of Governors referred Iran's nuclear file to the UN Security Council over its failure to comply with requirements concerning its nuclear activities.
Inspectors have not been able to verify the condition or whereabouts of Iran's stockpile of near-weapons-grade uranium since June 2025, when Israel and the US struck Iranian nuclear facilities.
President Donald Trump has repeatedly warned Iran against carrying out nuclear activity at Pickaxe Mountain.
Speaking at a Republican rally in Texas on Wednesday, Trump said the US had observed activity at the facility and warned Iran that it would face a powerful response if the activity continued.
“We notice there's a little activity at Pickaxe. I would advise Iran not to get cute, because we will have to hit them very hard," Trump said.
Trump issued a similar warning last week, telling reporters in the Oval Office that Iran would not be permitted to obtain a nuclear weapon and raising the possibility of an American strike on the site if nuclear activity was taking place there.
The Pickaxe Mountain facility, located in the Zagros Mountains, was developed following an attack on an Iranian centrifuge workshop six years ago. Grossi said Iranian officials had indicated at the time that nuclear-related infrastructure would be moved into tunnels inside a mountain in order to protect it from attacks.
Israel and the US have demanded that Iran dismantle its centrifuge program and halt uranium enrichment.
The IAEA's censure resolution against Iran could pave the way for additional military strikes on Iranian nuclear facilities. Trump has repeatedly said that preventing Iran from obtaining a nuclear weapon is the reason for the war with the Islamic Republic.
Iran, meanwhile, warned Western countries this week against using the IAEA as an instrument of war. In a diplomatic document, Iran's representative to the agency pointed to the June 2025 attacks, which began shortly after the IAEA found Iran in violation of its nuclear obligations, and called on diplomats to condemn the strikes.
Grossi also expressed growing concern over countries reconsidering whether to acquire or potentially use nuclear weapons, linking the trend to an international environment marked by increasing conflict and war.
He warned that further nuclear proliferation could ultimately lead to the use of nuclear weapons.