A U.S. Navy coastal patrol ship changed course after a fast-attack craft from Iran’s Islamic Revolutionary Guard Corps came within 100 yards (91 meters) of it in the central Gulf on Sunday, two U.S. Defense Department officials told Reuters on Tuesday. It was at least the fourth such incident in less than a month. U.S. officials are concerned that these actions by Iran could lead to mistakes.

Years of mutual animosity eased when Washington lifted sanctions on Tehran in January after a deal to curb Iran’s nuclear ambitions. But serious differences still remain over Iran’s ballistic missile program, and over conflicts in Syria and Iraq. The officials, speaking on condition of anonymity, said the Iranian vessel sailed directly in front of the USS Firebolt, forcing the 174-foot (53-metre) U.S. ship to change course. READ MORE