(REUTERS) – A U.S. Navy destroyer fired three warning shots towards four of Iran’s Islamic Revolutionary Guard Corps vessels on Sunday after they closed in at a high rate of speed in the Strait of Hormuz, two U.S. defense officials told Reuters on Monday.

The officials, speaking on the condition of anonymity, said the USS Mahan established radio communication with the boats but they did not respond to requests to slow down and instead continued asking the Mahan questions. The Navy destroyer fired warning flares and a U.S. Navy helicopter also dropped a smoke float before the warning shots were fired.

The Iranian vessels came within 900 yards (800 meters) of the Mahan, which was escorting two other U.S. military ships, they said.

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