The United States is warning shipping companies that they could face sanctions for making payments to Iran in exchange for safe passage through the Strait of Hormuz. The warning from the United States Treasury Department increases pressure in the growing standoff over control of the vital waterway, where about one fifth of the world's oil and natural gas trade normally passes.

Iran effectively closed the strait after launching attacks and issuing threats against ships following the outbreak of war involving the United States and Israel on February 28. Tehran later began offering select vessels alternative routes closer to its coastline, at times charging fees for transit.

According to the United States, these payments may take many forms, including cash, digital assets, informal swaps, charitable donations, or payments made at Iranian embassies. In response to the closure, the United States imposed a naval blockade on Iranian ports on April 13, preventing Iranian tankers from departing and restricting a key source of revenue for Iran. Since the blockade began, dozens of commercial ships have reportedly been instructed to turn around.