An earlier incident on April 2 marked the first time in more than a year that Iranian vessels have harassed American ships in the area.
The incident Monday night occurred as three Iranian Islamic Revolutionary Guard Corps Navy (IRGCN) speedboats approached the U.S. Navy patrol craft USS Firebolt and the U.S. Coast Guard cutter Baranoff operating in the northern Persian Gulf.
The three Iranian boats rapidly approached the two American ships at what a U.S. Navy spokesperson called "an unnecessarily close range, with unknown intent" coming as close as 68 yards to both ships.
"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," said Cmdr. Rebecca Rebarich, a spokesperson for the Navy's 5th Fleet, which oversees U.S. Naval operations in the Middle East.
"The crew of Firebolt then fired warning shots and the IRGCN vessels moved away to a safe distance from the U.S. vessels," she added.
Rebarich said that the actions of the three Iranian boats "increased the risk of miscalculation and/or collision" and did not follow the maritime "rules of the road."
The characterization of Monday's incident was different than the April 2 incident that the Navy characterized as "unsafe and unprofessional."
"We do not assess this is a new trend," Rebarich said of both incidents. "We assess every interaction based on the facts and circumstances."
She noted that in the April 2 incident, the IRGCN catamaran Harth 55 conducted "aggressive, unsafe, harassing maneuvers against our ships" while the intent of the three Iranian craft in Monday's incident was "unclear"
The Harth 55 repeatedly crossed in front of the U.S. Coast Guard Cutters Wrangell and the Monomoy on April 2, while both ships were operating in the northern Persian Gulf. At one point the Harth came as close as 70 yards to the American ships.
"The Harth 55 closed aggressively on Wrangell’s bow, resulting in Wrangell maneuvering to avoid collision while sounding five short blasts from the ship’s horn," said Rebarich.
The crew of the Harth responded to bridge-to-bridge radio warnings from the American vessels but "they continued the unsafe maneuvers," Rebarich said.
"After approximately three hours of the U.S. issuing warnings and conducting defensive maneuvers, the IRGCN vessels maneuvered away from the U.S. ships and opened distance between them," she added.
Iranian craft harassing American military vessels has become a routine occurrence in recent years, but U.S. officials were unclear as to why Iran seemed to pause those activities over the past year.
U.S. Coast Guard ships have operated in the Persian Gulf since 2003 and fall under the control of U.S. Naval Forces Central Command’s Task Force 55.