The trouble flared up when the US Coast Guard fired 30 warning shots after 13 Iranian armed speedboats in the Strait of Hormuz. Pentagon spokesman John Kirby said the US took action after some of the Iranian fast boats came within 150 yards of six US military vessels escorting the guided-missile submarine Georgia.
The flare-up was the second time in two weeks that a US ship has opened fire to warn off vessels from Iran’s paramilitary Revolutionary Guard.
Mr Kirby said: “They were acting very aggressively.”
The Coast Guard cutter fired the warning shots from a .50 caliber machine gun before the Iranian vessels left, he added.
He declined to comment on questions over whether the Revolutionary Guard are trying to pick a fight with the US Navy.
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The guided missile cruiser USS Monterey was in the convoy.
Just a day earlier, the Monterey had intercepted an arms shipment aboard a ship in the Arabian Sea.
It was apparently headed for Yemen, whose Houthi rebels – which Iran supports – are involved in a bloody civil war against the government.
In yesterday’s incident, two Iranian boats broke away from the others and moved to the other side of the US formation.
They then sped towards some of the American ships.
In an attempt to warn them off, the US issued repeated bridge-to-bridge verbal warnings, said Navy Cmdr. Rebecca Rebarich, a Navy 5th Fleet spokeswoman.
But when that failed and they moved with 300 yards, the Coast Guard cutter Maui fired a volley of warning shots from its .50-caliber machine gun.
It fired another volley when the Iranian boats got within 150 yards.
The two Iranian boats then “altered course and increased their distance from the US forces,” Ms Rebarich said.
Asked if the US vessels were allowed to fire directly on the Iranian boats and sink them, Mr Kirby declined to describe their rules of engagement.
However, he added: “They have the right of self defense and they know how to use that.”
Mr Kirby also pointed out that the Iranian actions took place in the Strait of Hormuz, where ships have little room to move.
He said: “It’s an international waterway and of course when you’re in the strait, there are certain limits to your ability to manoeuvre.
“It is a choke point in the region. So it’s not insignificant that this kind of dangerous, unsafe and unprofessional behaviour occurred there.”
On April 26, an American warship fired warning shots when vessels from Iran´s Revolutionary Guard came too close to a patrol in the Persian Gulf.
That was the first such shooting in nearly four years.