WASHINGTON — US President Donald Trump said Tuesday that a US Apache helicopter that crashed off the coast of Oman on Monday had been shot down by Iran and vowed retaliation amid a tenuous ceasefire.“I have just been informed by our great military that last night the Iranians shot down one of our highly sophisticated Apache helicopters while patrolling over the Strait of Hormuz,” Trump wrote on social media.“There were two pilots involved, both are safe and uninjured. Nevertheless, the United States must, of necessity, respond to this attack,” the president wrote.The US Navy rescued the Apache helicopter’s two crew members off Oman’s coast on Monday, the Pentagon’s Middle East command confirmed Tuesday.US Navy teams rescued the two crew members using an unmanned drone boat after a search assisted by US Air Force assets and elements of the Army’s 82nd Airborne Division, officials with US Central Command said.“The drone picked them up and transported them to another location on the water where they were then hoisted up to a helicopter for further transport,” US CENTCOM spokesperson Tim Hawkins told Al-Monitor. The US military began fielding Corsair sea drones in the Middle East in March, he said.The incident came just a day after Iran and Israel briefly resumed fighting with mutual strikes on Sunday despite public admonishment from the Trump White House, which is seeking a negotiated end to the war with Tehran.It was not immediately clear how the Apache was brought down. In March, US Defense Secretary Pete Hegseth said the military would have “complete control” over Iran’s airspace “within days.”Yet Iran has shot down at least 24 and as many as 30 US MQ-9 drones during the war, roughly a fifth of the Pentagon’s fleet, at an estimated cost of more than $1 billion.Iran has also previously shot down a US F-15 over its territory, leading to an extended rescue operation involving several hundred US troops deep within Iranian territory in April.Hours prior to the shoot-down on Monday, an F/A-18 Super Hornet launched from the aircraft carrier USS Abraham Lincoln fired a missile into the “engineering and steering spaces” of a commercial tanker, the M/T Marivex, in the Gulf of Oman after its crew attempted to breach the US blockade of Iran’s ports, CENTCOM said.It was not immediately clear whether there was any direct connection between the Apache crash and the US airstrike on the Marivex, which has been under US economic sanction over its links to Iran’s oil exports abroad. The Marivex was the seventh commercial vessel disabled by the US military in the Gulf region since the US initiated its blockade of Iran’s ports on April 13. Iran has recently attempted to retaliate for such strikes by launching drones into the Strait of Hormuz, leading to additional US airstrikes on Iranian soil despite Pentagon officials saying the ceasefire remains in place.US naval and air assets have been remotely advising the crews of commercial tanker and cargo vessels stuck in the Persian Gulf due to Iran’s blockade of the Strait of Hormuz. Last month, Trump threatened to bomb Oman, a US-aligned Gulf state and erstwhile mediator in the conflict with Iran, if its government collaborates with Iran's stated plans to impose tolls on ships transiting Hormuz.