WASHINGTON — Four Iranian small boats harassed a U.S. Navy warship near the Persian Gulf, but no missiles were fired, the chief of naval operations said Wednesday.

Adm. John Richardson said the incident involving the guided missile destroyer USS Nitze reflects the greater competition the U.S. is facing at sea. He added it underscores the naval tensions with Tehran, which include other similar incidents as well as the brief detention in January of 10 U.S. Navy sailors who mistakenly steered into Iranian waters.

A U.S. defense official said the Iranian boats approached the Nitze at high speed on Wednesday, in an unsafe and unprofessional manner. The destroyer fired ten flares in the direction of the Iranian boats and sounded the ship’s whistle several times in an effort to warn the boats away, the official said. The Nitze also tried to communicate with the Iranians over the radio, and also changed course to avoid the vessels.

The official said two boats ignored the warnings and continued to speed toward the Nitze until they were within 300 yards of the U.S. ship.

The USS Nitze was in international waters in the Strait of Hormuz with the USS Mason, also a guided missile destroyer. The official wasn’t authorized to discuss the incident publicly so spoke anonymously.

Richardson said the encounter raises questions about what is the “new normal,” adding, “We have to be mindful that we don’t become complacent as things get steadily busier, steadily more engaging and that we’re thoughtful about how we approach those challenges.”

Last December, Iranian ships fired rockets near U.S. warship and other vessels in the Strait of Hormuz, and a month later flew an unarmed drone over the USS Harry S. Truman aircraft carrier in the Persian Gulf.

The January detention incident triggered a Navy investigation which found that the sailors failed to navigate properly and did not use appropriate communications as they sailed near Farsi Island, a base for the Iran Revolutionary Guard Corps Navy in the Persian Gulf.

The Iranians boarded the boats, pointed their guns at the U.S. sailors and took them to the island where they were held overnight. They were released after Washington intervened.

Several of the sailors were fired from their jobs or disciplined in connection with the incident.