Iranian media say that the country's navy has warned a U.S. warship to leave an area in the Gulf of Oman where Iran has been conducting a naval drill.
Iran's semi-official Fars news agency quoted Iranian Navy chief Admiral Habibollah Sayyari as saying that the U.S. warship received two warnings before leaving the area.
Iran on January 27 began a naval drill near the Strait of Hormuz, through which one-fifth of the world's oil supply passes.
The warning was the first such incident since 10 U.S. sailors were briefly captured by Iran on January 13 after drifting into Iranian territorial waters.
There was no immediate reaction from Washington, which this month joined other world powers in lifting sanctions on Iran after the implementation of an international deal to curtain Tehran's nuclear program.