WASHINGTON—The U.S. Navy fired on a commercial vessel in international waters off Iran's coast after the ship attempted to breach Washington's blockade on Iranian ports, marking a direct enforcement of U.S. sanctions and a sharp escalation in the standoff between Washington and Tehran.

The incident is a central piece of President Trump's maximum pressure campaign against Iran, a policy designed to cut Tehran's oil exports and block imports of strategic materials—starving its nuclear program and curbing its regional influence. The vessel's flag state and cargo remain undisclosed.

The firing follows months of heightened rhetoric and expanded U.S. naval deployments in the Persian Gulf. U.S. Central Command has previously warned against illicit shipping operations supporting the Iranian regime. Analysts said the action could drive up maritime insurance rates for commercial vessels near the Strait of Hormuz, a critical chokepoint for global oil shipments.

Tighter blockade enforcement could further constrict global oil supply and push crude prices higher, benefiting oil-producing nations and energy companies outside Iran while raising costs for consumers worldwide.

Iran's Foreign Ministry had not issued a formal statement but was expected to condemn the action as a violation of international law. The United States has consistently defended its authority to enforce sanctions against entities facilitating Iranian trade.

The United Nations Security Council was expected to convene an emergency session within 48 hours. Secretary of State Michael Pompeo was scheduled to brief reporters the following morning on the administration's justification for the engagement and its next steps on Iran policy.