The U.S. military is due to begin a blockade of ships entering or leaving Iran’s ports at 10 a.m. (1400 GMT), after weekend talks on ending the war broke down, Reuters reports.
Tehran has threatened to retaliate against ports of its Gulf neighbors.
The ceasefire, which halted six weeks of U.S. and Israeli airstrikes, is under threat, with only a week left to run.
Oil prices surged when trade reopened on Monday, with no sign of a swift reopening of the Strait of Hormuz to ease the biggest ever disruption in supplies.
An Iranian military spokesperson called any U.S. restrictions on international shipping “piracy,” warning that if Iranian ports were threatened, no port in the Gulf or Gulf of Oman would be secure. Any military vessels approaching the strait would violate the ceasefire, Iran’s Revolutionary Guards said.
