Washington DC - President Donald Trump vowed on Tuesday to respond after he accused Iran of shooting down a US military helicopter the previous night, hours after he said negotiations to end the Middle East war were in their final stages.

Mohammad Bagher Ghalibaf, Iran's parliament speaker and its chief negotiator in talks with Washington, meanwhile warned the US on Tuesday against breaking its "commitments."

The comments came a day after Iran and Israel halted attacks that threatened to reignite the regional war, which was sparked by US and Israeli strikes on Iran on February 28.

In a statement, Trump said he had been informed "that last night the Iranians shot down one of our highly sophisticated Apache Helicopters while patrolling over the Strait of Hormuz."

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While the crew members were uninjured, "the United States must, of necessity, respond to this attack," he said.

Iran's Ghalibaf also issued a warning on Tuesday.

"We prefer the language of diplomacy, but we speak other languages far more fluently. Break your commitments, and we'll switch to what we speak best. You ride the horse you saddled!" he said on X.

The Apache helicopter is the second crewed aircraft that Washington has confirmed was shot down by Iran during the war, following the loss of an F-15 fighter plane in April.