Iranian warplanes warned off two "coalition vessels" during military drill in waters off the country's southeast, a senior naval officer said, in the latest confrontation between Iranian and western forces that patrol the Gulf.
The vessels approached the area of the drills early on Monday to monitor Iranian ships, said Rear Admiral Mahmoud Mousavi, spokesman for the drills, according to Tasnim news agency.
"Iranian drones identified the vessels, then Iranian planes flew over them and gave them a warning. The vessels left the area," he was quoted as saying.
The Iranian army launched two days of exercises on Monday involving ground, naval and air forces in the country's south and southeast, near the Makran Coast, and other areas in the Gulf of Oman.
There have been periodic confrontations between the Iranian and US military in the Gulf - a major trade route for oil - in recent years.
In the first such incident since President Donald Trump took office, a US Navy ship fired warning shots when an Iranian vessel approached to within 450 feet (140 meters) last July.
The following month an unarmed Iranian drone came within 100 feet (30 meters) of a US Navy warplane as it prepared to land on an aircraft carrier in the Gulf.
During the presidential campaign last September, Trump said any Iranian vessel that harassed the US Navy in the Gulf would be "shot out of the water".