Iran struck a vessel in the Strait of Hormuz on Thursday, forcing a pause on evacuations of stranded seafarers and demonstrating its continued ability to restrict the critical waterway, despite the agreement reached last week with the United States.

A US official told CNN the vessel was attacked by an Iranian drone, but did not provide further details.

While Iran has not claimed responsibility, Thursday’s attack came hours after its powerful revolutionary guards warned that vessels would only be given safe passage via Iranian routes, challenging the Trump administration’s claim that the strait is free and open once more.