WASHINGTON — The United States on Monday declared maritime superiority over the Strait of Hormuz, through which approximately 20 percent of the world's oil passes daily, using legal authorities derived from the United Nations Convention on the Law of the Sea, a treaty the United States has not ratified.

The declaration came in response to Iran's existing blockade of the same waterway, which Tehran has maintained since late February under legal authorities also derived from the United Nations Convention on the Law of the Sea, a treaty Iran has also not ratified.

Both parties confirmed they remain fully committed to their respective interpretations of the framework.

"The United States Navy, the Finest in the World, will begin the process of BLOCKADING any and all Ships," President Trump announced on Truth Social, adding that vessels found to have paid Iran's $2 million transit toll would be interdicted in international waters. Iran's Revolutionary Guards Naval Command responded that enemies would be "trapped in a deadly vortex" should they miscalculate, a statement issued through the same international communications infrastructure both nations use to dispute each other's legal standing.

The shipping lanes in question lie entirely within the territorial waters of Oman, according to the International Maritime Organization's Traffic Separation Scheme and a bilateral treaty signed by Iran and Oman in July 1974. Oman is not a party to the current conflict. Iran's parliamentary commission voted in March 2026 to impose tolls on vessels transiting what it described as Iranian waters. A deputy parliament speaker clarified that fees must be paid in Iranian rials, though a separate proposal to collect $1 per barrel in cryptocurrency was also reported to be under consideration, described by diplomatic observers as the "Ayatoll booth."

China, which sourced 13.4 percent of its oil imports from Iran last year according to Reuters, called the US blockade "dangerous and irresponsible." Russia vetoed the UN Security Council resolution condemning Iran's blockade of the strait, then announced it stood ready to mediate. Russian Foreign Minister Sergey Lavrov arrived in Beijing following the US blockade announcement.

The United Kingdom, France, and Germany publicly distanced themselves from the US operation. Italy denied the US access to a key airbase. Spain blocked US use of its airspace for military operations. Prime Minister Keir Starmer confirmed the UK would not participate, though he agreed to co-chair a conference on restoring freedom of navigation, which is the stated goal of both blockades.

US Vice President JD Vance, departing Islamabad after 21 hours of talks he described as having gone "well" on "most points," said Washington had delivered its "final and best offer." The ceasefire the offer was intended to extend expires April 22.

The Vienna Convention on the Law of Treaties, described in legal literature as "the mother of all treaties," holds that signatories are obliged to refrain from acts defeating the purpose of a treaty even absent ratification. Both the United States and Iran have signed the Vienna Convention. Neither has ratified it.