A US patrol boat fired warning shots at Iranian gunboats in the Persian Gulf after they approached at rapid speed and came within an "unnecessarily close range with unknown intent," the Navy said on Tuesday.
The Islamic Revolutionary Guard Corps Navy (IRGCN) ships closed within as little as 68 yards (62 meters) from the USS Firebolt and the USCGC Baranoff while the US ships "were conducting routine maritime security operations in international waters" late Monday, said the Navy.
"The U.S. crews issued multiple warnings via bridge-to-bridge radio and loud-hailer devices, but the IRGCN vessels continued their close range maneuvers," it said. "The crew of Firebolt then fired warning shots, and the IRGCN vessels moved away to a safe distance from the U.S. vessels."
The Firebolt is a US Navy patrol boat while the Baranoff is a Coast Guard patrol boat.
The last time the US fired warning shots at Iranian ships was in July 2017, nearly four years ago.
The incident on Monday comes as the US and Iran are engaged in indirect talks in Vienna about efforts to bring both nations back into compliance with the 2015 nuclear accord that former US President Donald Trump withdrew from three years later.
Trump's decision, made against the recommendations of all other deal participants, preceded his additional steps to impose economic sanctions on Iran lifted under the Joint Comprehensive Plan of Action.
Iran in turn drew down from its nuclear commitments, hoping to apply pressure on the deal's other signatories.