The White House has expressed concern after several close encounters between Iranian vessels and U.S. warships in the Persian Gulf this week.
A White House spokesman said such incidents are cause for concern and increase risks of miscalculation.
Josh Earnest said on August 26 the behavior is unacceptable and "in a compressed space like the Strait of Hormuz it increases the risk associated with possible miscalculations."
U.S. Defense officials said on August 25 that a U.S. Navy ship fired warning shots after an Iranian fast-attack craft approached two U.S. ships in the northern Gulf.
The incident, which happened on August 24, started with three Iranian vessels, but there was only one around by the time the warning shots were fired, U.S. officials said.
Another interaction took place between an Iranian and U.S. ship on August 24, although U.S. defense officials disclosed few details on that incident.
Iranian Defense Minister Hossein Dehghan said the Iranian vessels were just doing their job.
"If an American ship enters Iran's maritime region, it will definitely get a warning. We will monitor them and, if they violate our waters, we will confront them," Dehghan said in a statement.
Based on reporting by AP and Reuters