WASHINGTON (REUTERS) - Four vessels from Iran's Islamic Revolutionary Guard Corps (IRGC) "harassed" a US destroyer on Tuesday (Aug 23) by carrying out a "high speed intercept" in the vicinity of the Strait of Hormuz, a US defence official said on Wednesday (Aug 24), amid Washington's concerns about Iran's posture in the Gulf and in the Syrian civil war.
The official, speaking on the condition of anonymity, said two of the Iranian vessels came within 275m of the USS Nitze in an incident that was "unsafe and unprofessional". The vessels harassed the destroyer by "conducting a high speed intercept and closing within a short distance of Nitze, despite repeated warnings", the official said.
The US defence official said that in Tuesday's incident the USS Nitze tried to communicate with the Iranian vessels 12 times, but received no response. It also fired 10 flares in the direction of two of the Iranian vessels.
"The Iranian high rate of closure... created a dangerous, harassing situation that could have led to further escalation, including additional defensive measures by Nitze," the official said.
The USS Nitze had to alter course in order to increase its distance from the Iranian vessels, the official said. The official said the incident could have led to a diplomat protest, but the United States does not have diplomatic relations with Iran.
It remains to be seen whether these actions were carried out by rogue Revolutionary Guard commanders or sanctioned by senior officials in Teheran, said Mr Karim Sadjadpour, an Iran expert at the Carnegie Endowment for International Peace.
"For four decades the Revolutionary Guard have been told that America is the greatest threat to the Islamic Revolution,"said Mr Sadjadpour. "This institutional culture hasn't changed after the nuclear deal," he added.
The IRGC, the Islamic Republic's praetorian guard, is suspicious of US military activity near Iran's borders and appears to be sticking to a familiar posture in the Gulf that predates last year's nuclear accord between Iran and six world powers. including the United States.
The Guards operate land and naval units separate from the regular armed forces and stage frequent war games in the Gulf, which separates Iran from its regional rival Saudi Arabia and a US naval base in Bahrain.
In January, 10 US sailors, who were aboard two patrol craft, were detained by the IRGC when they inadvertently entered Iranian territorial waters. They were released the next day after being held for about 15 hours.