The Strait of Hormuz, a strategic chokepoint at the mouth of the Persian Gulf, has once again become a flashpoint as Iran plans a military drill that could intersect a key international shipping lane.

Iran has warned vessels that a live-fire exercise will take place Sunday and Monday in the strait, through which about one-fifth of the world’s oil supply passes. The U.S. Central Command issued a warning, cautioning Tehran that “unsafe and unprofessional behavior” near American forces, regional partners, or commercial ships could raise the risk of collisions, escalation, and destabilization.

The strait, just 33 kilometers (21 miles) at its narrowest point, links the Persian Gulf to the Gulf of Oman. While Iran and Oman control portions of its waters, it is considered an international waterway. Historically, it has been vital for trade and today carries the majority of Persian Gulf oil to Asian markets. Although pipelines in Saudi Arabia and the UAE can bypass it, most volumes have no alternative route. Past threats to the strait have spiked global energy prices, including during Israel’s 12-day war against Iran in June.

Iran’s notice to mariners indicated the drill may enter the Traffic Separation Scheme, a two-lane system guiding ships in and out of the Gulf. It is expected to involve the paramilitary Revolutionary Guard, whose small fast-attack vessels frequently confront U.S. Navy ships.

Tensions are heightened by U.S. concerns over Iran’s violent crackdown on nationwide protests and its nuclear program. President Donald Trump has threatened military action if Iran crosses red lines, including killing protesters or executing detainees. The USS Abraham Lincoln and supporting vessels are in the Arabian Sea, ready to respond if ordered. Iran has warned of possible retaliatory strikes against U.S. interests and Israel.

The situation underscores the Strait of Hormuz’s continuing strategic importance and the potential risks to global energy supplies as both sides maintain a show of force in the region.