(NEW YORK) — A U.S. Coast Guard cutter fired 30 warning shots at two armed Iranian fast-attack boats on Monday after they approached American warships at a high rate of speed while transiting through the Strait of Hormuz, according to the U.S. Navy.

It is the second time in as many weeks that American ships have had to fire warning rounds at Iranian speedboats that engaged in what the Navy called “unsafe” and “unprofessional” behavior near the Persian Gulf.

The two Iranian boats were part of a larger group of 13 fast-attack boats from the Islamic Revolutionary Guard Corps Navy (IRGCN) that made what the U.S. Navy’s 5th Fleet called “a high-speed approach” on six American ships.

At the time, the guided-missile cruiser USS Monterey, patrol coastal ships USS Thunderbolt, USS Hurricane, USS Squall and Coast Guard patrol boats USCGC Wrangell and USCGC Maui were escorting the guided-missile submarine USS Georgia through the Strait of Hormuz, the narrow waterway separating the Persian Gulf and the Arabian Sea.

“Two of the 13 IRGCN vessels broke away from the larger group, transited to the opposite side of the U.S. formation and approached Maui and Squall from behind at a high rate of speed (in excess of 32 knots) with their weapons uncovered and manned,” according to a Navy statement. “The remaining 11 FIAC maintained position which places the formation of the U.S. ships in between the two IRGCN groups.”

The crew of the Coast Guard cutter Maui fired two warning-shot volleys from its .50-caliber machine gun at the two speed boats after they ignored acoustic device warnings — horn blasts and bridge-to-bridge radio communications from the American vessels.

The Iranian boats did not break away from the American ships until after a second volley of warning shots were fired as they approached to a distance of 150 yards and at a high rate of speed.

The Navy statement labeled the warning shots as “lawful de-escalatory measures.”

At a briefing with reporters on Monday, Pentagon spokesman John Kirby labeled the action by the Iranian boats as “unsafe” and “unprofessional” and “dangerous.”

The Navy described the approach by the two Iranian boats to within 150 yards as “an unnecessarily close range that put the ships and their crews in immediate danger.”

Monday’s incident was the third close encounter between Iranian boats and American warships in the last five weeks.

Once a regular occurrence, Iran’s harassment of American Navy ships in the Persian Gulf had ceased over the past year until an April 2 incident involving Iranian boats that swarmed two U.S. Coast Guard cutters.

The second incident on April 27 led the Navy patrol boat USS Firebolt to fire warning shots at three Iranian small boats that had closed to within 68 yards of the U.S. Coast Guard cutter Baranoff.

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.

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