A United States Navy destroyer fired warning shots at Iranian patrol vessels rushing and threatening to ram the American warship. U.S. defense officials said Monday.

The incident happened Sunday inside the Strait of Hormuz, the narrow waterway at the entrance to the Gulf.

Approaching fast, 4 Iranian fast attack boat, heading towards USS Mahan-72

Navy Capt. Jeff Davis, a Pentagon spokesman, said after failing to establish radio communication, firing smoke flares, used an audible siren, flashing lights and a ship’s whistle to warn the approaching four fast-attack boats of the Iranian Revolutionary Guard Corps (IRGC).

U.S sailors fired warning shot at 4 approaching Iranian attack boat.

The USS Mahan immediately fired three warning shots from a distance of 900 yards with a .50-caliber machine gun, forcing them to break course.

Davis said, at the time of engagement the USS Mahan was with two other US navy ships, the USNS Walter S. Diehl and the amphibious assault ship USS Makin Island cruising through the Strait of Hormuz which is a narrow waterway in the Persian Gulf through which a significant amount of the world’s oil passes through.

The IRGC is a paramilitary wing separate from the conventional Iranian Navy which is specifically loyal to Supreme Leader Ali Khamenei.

Davis said, “This was an unsafe and unprofessional interaction.”

The engagement is the most recent in a year-long series of maritime engagements amongst Iran and the U.S. in the Persian Gulf.

Similar incidents took place in 2015 and early 2016, wherein an Iranians briefly captured the crew of two small US patrol boats that strayed into Iranian waters. Later released after 24 hours.

Reflecting a more hardline side of Iran’s leadership. Its IRGC naval forces typically acted more aggressively and harsh to ships passing in the Gulf more specifically to U.S. ships than the conventional Iranian navy.

Iran has two naval forces: the Islamic Republic of Iran Navy, or IRIN, and the Islamic Revolutionary GuardCorps Navy, or IRGCN. The IRIN is the naval branch of Iran’s, Artesh the traditional military force that existed prior to the 1979 revolution.-JCE.