Officials say a U.S. Navy ship fired warning shots when an Iranian vessel in the Persian Gulf came within 150 yards on Tuesday, July 25. (Reuters)

A U.S. Navy patrol boat fired two bursts of machine-gun fire at an Iranian military ship Tuesday as it made an alarmingly fast and close approach in the Persian Gulf, marking the latest aggressive encounter between the two adversaries.

The unidentified Iranian Revolutionary Guard vessel got within 150 yards of the USS Thunderbolt and risked a collision, U.S. officials said, before the American patrol boat fired warning shots and quickly ended the encounter.

One Pentagon official who spoke to The Washington Post on the condition of anonymity described it as an isolated incident and confirmed that no one was hurt.

U.S. officials have not specified where the incident occurred, saying only that U.S. and coalition ships were participating in a daytime training exercise when the Iranians conducted an “unsafe and unprofessional interaction” by failing to observe internationally recognized maritime customs.

It’s also unclear how many Americans were aboard the Thunderbolt. Based in Norfolk, it can carry a crew of 27 and is used primarily for patrolling coastlines and to provide surveillance for interdiction operations.

U.S. officials have not yet disclosed what type of weapons the crew fired, although the ship is armed with .50-caliber machine guns and MK-38 chain guns in addition to automatic grenade launchers.

At least three other American vessels were nearby at the time.

Video released by the U.S. Central Command shows the Iranian vessel approaching the Thunderbolt’s starboard side, extremely close to the ship’s bow. An American sailor can be heard radioing the ships’ coordinates, and then the sound of machine-gun fire.

“The Iranian vessel did not respond to repeated attempts to establish radio communications as it approached,” said Maj. Adrian Rankine-Galloway, a Defense Department spokesman. “Thunderbolt then fired warning flares and sounded the internationally recognized danger signal of five short blasts on the ship’s whistle, but the Iranian vessel continued inbound. As the Iranian vessel proceeded toward the U.S. ship, Thunderbolt again sounded five short blasts before firing warning shots in front of the Iranian vessel.”

Iranian military officials characterized the incident as a U.S. provocation and took credit for having “neutralized” the threat.

In a report published last winter, the Office of Naval Intelligence indicated that vessels operated by the Revolutionary Guard Corps routinely monitor U.S. and allied warships in the Persian Gulf and the Strait of Hormuz, a busy waterway that links to the Gulf of Oman. The majority of these encounters are “safe and routine,” it said, but “unprofessional or aggressive” run-ins are becoming more frequent.

“Such operations increase the likelihood for a mishap at sea, potentially leading to strategic tension and insecurity in the region,” the report said.

The Pentagon documented 35 such interactions with Iranians last year, up from to 23 in 2015. This year, it has acknowledged at least five.

Last month, Iranian forces harassed a formation of three American ships — the amphibious assault ship Bataan, the guided-missile destroyer Cole and the dry cargo ship Washington Chambers — shining floodlights on them from a distance of 800 yards and pointing a laser at an airborne U.S. helicopter.

Twice in March, the USNS Invincible, which is outfitted with sonar and radar equipment, had close encounters. In one incident, an Iranian frigate moved within 150 yards. In the other, Revolutionary Guard fast boats cut in front of the U.S. ship, forcing it to rapidly change course to avoid a collision.

Such adversarial behavior between the two nations’ navies comes amid what has become a more complicated dynamic on the ground inside Iraq and Syria.

Speaking at a security forum in Colorado last week, the head of U.S. Special Operations Command, Army Gen. Raymond A. “Tony” Thomas, acknowledged how American troops now routinely come “coffee-breath close” to Iranian-backed forces, according to CNN.

Last month in Syria, where fighters trained by Iran are supporting President Bashar al-Assad, U.S. forces shot down at least two armed Iranian drones near the border with Iraq and Jordan.

Thomas noted, too, that during one recent trip into northern Iraq, where Iranian-trained militias are battling the Islamic State, his plane was parked beside one belonging to Maj. Gen. Qasem Soleimani, commander of the Revolutionary Guard’s special operations Quds Force, which the United States has designated a supporter of terrorism.

“We bump into them everywhere,” he said.

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