WASHINGTON -- Three more close encounters have been reported between US Navy warships and vessels operated by Iran's Islamic Revolutionary Guard Corps navy (IRGCN). In one instance, a US warship fired warning shots at an Iranian vessel.

And in an incident taking place Aug. 15, Guards vessels launched rockets in exercises a few miles away from two US Navy ships.

The latest incidents took place Wednesday in the northern Persian Gulf, US defense officials reported today. They follow Tuesday's incident near the Strait of Hormuz when high-speed vessels approached two US Navy destroyers.

In the first incident, as reported by US defense officials, the US patrol coastal ships Tempest and Squall were patrolling in international waters in the northern Gulf. Three IRGCN vessels approached at high speed and crossed the bow of the Tempest at 600 yards on three separate occasions. Tempest sounded five short blasts from the ship's whistle, indicating the maneuvers were unsafe, and attempted to establish radio communications, apparently without success.

Later that same day Tempest and Squall were harassed by an Iranian Naser-class patrol boat, of a type known to be operated by the Guards. That vessel approached Tempest head-on to within 200 yards, said Cmdr. Bill Urban, a spokesman for the US Navy's Central Command (NAVCENT) in Bahrain.

"This situation presented a drastically increased risk of collision," Urban said, "and the Iranian vessel refused to safely maneuver in accordance with internationally recognized maritime rules of the road, despite several request and warnings via radio, and visual and audible warnings from both US ships." 

During the encounter Tempest fired three warning flares in the direction of the vessel, Urban said, while also attempting radio communications and sounding loud audible warnings via loudspeaker.

Squall fired three warning shots from a .50-caliber gun and that caused the Iranian vessel to turn away.

The shots "were fired well in advance of the vessels," Urban said, adding that Squall took efforts to make sure the shots were fired clear of both the Iranian vessel and civilian traffic. "No one was injured or hit by the warning shots," he said.

In a third event, the destroyer Stout was underway in the northern Gulf when, Urban said, the same Naser vessel conducted an "unsafe intercept," crossing the bow of Stout three times "at close range." The destroyer, capable of much higher speeds than the Naser, maneuvered away from the vessel to avoid collision and, Urban added, "employed devices to discourage the IRGCN vessel from continuing their approach towards Stout." 

Urban also revealed that on Aug. 15, seven IRGCN vessels conducted a rocket firing exercise "in close proximity" to the destroyer Nitze and the Tempest in international waters in the central Gulf.

"The Iranian vessels were within 12,000 yards of Nitze and 5,000 yards of Tempest," Urban said. "The vessels were seen firing eight to nine rockets away from the US ships and did not notify them of the intent to conduct a live fire exercise."

NAVCENT, Urban said, "assessed all of these interactions as unsafe and unprofessional due to the Iranian vessels not abiding by international law and maritime standards, including the 1972 Convention on the International Regulations for Preventing Collisions at Sea (COLREGS) maritime 'Rules of the Road.'

"The Iranian high-rate-of-speed approaches towards three Unites States ships operating in international waters in accordance with international law along with multiple bow crossings at short range and the disregard of multiple warning attempts created a dangerous, harassing situation that could have led to further escalation," Urban said.

Of the rocket exercise, Urban noted that, "the unsafe exercise near U.S. ships operating in accordance with international law while transiting in international waters created a dangerous situation.

US officials noted the most recent series of incidents all have involved the Revolutionary Guards and not the Iranian navy. Navy-to-navy relations between the US and Iran, while by no means warm, are generally categorized by the US as professional. The Guards, also known as the Pasdaran, generally operate outside of Iran's military hierarchy.

The latest series of incidents follow another encounter that took place Tuesday at the southeastern end of the Gulf near the Strait of Hormuz, where four high-speed IRCGN craft approached the US destroyers Nitze and Mason. Two of the Iranian craft approached to within 300 yards of Nitze before the destroyers increased to high speed and pulled away.

Protests have not been filed over these incidents, said Cmdr. Bill Urban, a spokesman for the US Navy's Central Command (NAVCENT) command in Bahrain.

"The nature of this incident would have led NAVCENT recommend a diplomatic message of protest if this interaction had been with a country with which the United States had an official diplomatic relationship," Urban said, noting that the US has no official relations with Iran.