President Donald Trump on Tuesday said Iran shot down a US Apache helicopter that was patrolling the Strait of Hormuz overnight and vowed to respond, but gave no other details.
"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 in a social media post.
He said the two US pilots involved in the incident were both safe and uninjured.
"Nevertheless, the United States must, of necessity, respond to this attack," Trump added.
His remarks threw into deeper uncertainty the prospects for a truce announced on April 8 in the war.
On Monday, Israel and Iran said they would halt attacks on each other after an appeal by Trump to end their first direct exchanges of fire since April, but Tehran warned it would resume hostilities if Israel continued to attack its ally Hezbollah in Lebanon.
Monday's flare-up added further strain to efforts to broker a peace deal to end the wider Middle East war and reopen the Strait of Hormuz.
In remarks earlier on Tuesday about the downing of the Apache helicopter, Trump had said the two US helicopter crew members were "fine" following their rescue by a US Navy drone, but he had made no comment about what brought the Apache down.
A US Navy surface drone found and rescued the two crew, the US military told Reuters.
US Central Command said the AH-64 Apache went down at around 3:00 AM on Tuesday (2300 GMT on Monday).
In Tehran, two Iranian air defence personnel were due to be buried on Tuesday afternoon after being killed in Israeli strikes the day before, Iran's military said.
No deaths were reported in Israel after the Iranian strikes.
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