Both the US Coast Guard and the Iranian Navy have confirmed that a single shot was fired from the USCG cutter Monomoy late last month.
The shot was fired when an inflatable vessel from the Monomoy approached an Iranian dhow as part of normal security operations. When they USCG vessel got close to the Iranian vessel, they obsevered the dhow's crew training a .50 caliber machine gun on them and preparing to fire. The Monomoy fired a single warning shot into the air and did not strike the Iranian vessel. No one was injured in the incident.
Dhows are traditional wooden sailing vessels that are common off the coasts of Arabian and Asian countries. They have a crew from 12 - 30 and are commonly used for either fishing or trade.
The Monomoy is an Island-class patrol cutter commissioned in 1989, with her homeport at Coast Guard Station Woods Hole in Massachusetts. She is forward-deployed to Bahrain, and is currently serving as part of the United States Fifth Fleet.