Iran “made a very big mistake” in shooting down a US military surveillance drone over the Strait of Hormuz, President Donald Trump says.
However, he told reporters it could have been the result of human error, saying: “I find it hard to believe it was intentional.”
Iran said the drone had violated Iranian airspace, but the US military denied this.
The incident comes amid escalating tension between the two countries.
Iran’s Foreign Minister Javad Zarif said Iran would take its complaint that the US “encroaches on our territory” to the UN.
“We don’t seek war but will zealously defend our skies, land and waters,” he said on Twitter.
Speaking at the White House, he called the drone’s downing a “new fly in the ointment”.
Mr Trump said it was “documented” that the unmanned drone had been over international waters and not in Iranian airspace.
“I think probably Iran made a mistake – I would imagine it was a general or somebody that made a mistake in shooting that drone down,” he said.
“It could have been somebody who was loose and stupid,” he added.