The United States began enforcing a blockade of Iran’s ports and a partial restriction of the Strait of Hormuz at 10 a.m. EDT on Monday, escalating tensions following the collapse of recent peace negotiations.

The Strait of Hormuz, a critical chokepoint for global shipments of oil, fertilizer, and other essential goods, has become a focal point in the standoff between Washington and Tehran.

Iran warned it would respond if the blockade proceeds, calling the move illegal and likening it to piracy. Officials in Tehran cautioned that no Gulf port would be safe if access to Iranian ports is disrupted.

The escalation follows the breakdown of talks in Islamabad over the weekend, where U.S. and Iranian officials, with Pakistani mediation, failed to reach a peace agreement. U.S. Vice President JD Vance, who led the American delegation, said the primary obstacle was Iran’s refusal to abandon its nuclear program.

Diplomatic efforts are continuing despite the setback. Sources say Pakistan is working to bring both sides back to the negotiating table in hopes of securing an agreement before the current ceasefire expires next week.