The United States must respond after Iran shot down a US Army Apache helicopter over the Strait of Hormuz, President Donald Trump said on June 9, in an incident that threatens a fragile ceasefire.

The downing marks the first loss of an Apache since the war with Iran began in February and comes as Washington presses Tehran towards a deal to end the conflict and reopen the strait. Trump said both pilots had been rescued and were safe and uninjured, but that the United States would, of necessity, respond to the attack, without specifying what form that would take or when.

Trump made the accusation in a post on his Truth Social platform, saying the military had informed him Iran shot down the helicopter while it was patrolling over the strait.

US Central Command had earlier said the AH-64 Apache went down near the coast of Oman while patrolling regional waters, with the cause under investigation, and did not initially blame Iran. Two US officials said the aircraft was brought down by an Iranian drone.

The two crew members were rescued within about two hours by an uncrewed Navy surface vessel assigned to Task Force 59, in what officials described as the first such sea-drone rescue carried out by US forces.

Iran has not publicly claimed responsibility for the downing.

Apache helicopters have been a key asset in the US blockade of Iranian crude shipments and tankers, used to target small boats as Washington seeks to pressure Tehran into an agreement. The US military has lost dozens of aircraft since the war began in late February, according to a Congressional Research Service report.

Trump said the two sides were close to a deal that would halt Iran's nuclear programme and reopen the strait, repeating that an agreement could be signed within days.