The military action occurred as American forces seek to facilitate the transit of commercial shipping through the Strait of Hormuz in an effort dubbed "Project Freedom" that President Donald Trump announced on Sunday.

US Apache and Seahawk helicopters hit "six Iranian small boats threatening commercial shipping," Admiral Brad Cooper, the head of US Central Command (CENTCOM), told journalists.

US forces also "effectively engaged" all "missiles and drones that were fired at both us and the commercial ships," Cooper said.

Some cruise missiles were launched at US Navy ships but most of them as well as multiple drones targeted commercial vessels, he said.

"We defended both ourselves and, consistent with our commitment, we defended all the commercial ships," Cooper said.

US and Israeli forces launched a massive military campaign against Iran on February 28, prompting Iran to close the Strait of Hormuz -- a vital route for oil and gas exports -- while American forces later launched a blockade of Iranian ports.

Iranian state television said earlier Monday that the country's navy had fired cruise missiles, rockets and combat drones near US destroyers crossing the strait in what it described as a "warning shot."

CENTCOM said that two US guided-missile destroyers had passed through the strait into the Gulf as part of "Project Freedom," while two US-flagged merchant vessels transited the opposite way and "are safely headed on their journey."