Iran’s Supreme Leader Ali Khamenei has reportedly moved to a fortified underground bunker in Tehran amid rising fears of a potential U.S. attack.

The decision came after senior military officials assessed an increased threat level. The facility is described as a reinforced complex with interconnected tunnels, The Caspian Post reports via Iranian media.

Meanwhile, Khamenei’s third son, Masoud, is said to be managing the supreme leader’s office on a day-to-day basis and acting as the primary liaison with Iran’s executive branch.