Iran shot down a US drone near the Strait of Hormuz early on Thursday, amid rising tensions between Tehran and Washington.
The US military's Central Command said the drone, an RQ-4 Global Hawk, was downed in international airspace, describing it as an "unprovoked attack".
The drone was hit at 3.35am UAE time, according to a statement released by Centcom spokesman Navy Captain Bill Urban.
"Iranian reports that the aircraft was over Iran are false," Capt Urban said. "This was an unprovoked attack on a US surveillance asset in international airspace."
But the Islamic Revolutionary Guard Corps (IRGC) said it brought the drone down over Iranian territory after it violated Iranian airspace.
"The US-made Global Hawk surveillance drone was brought down" in Iran's southern coastal province of Hormozgan, according to Iranian Press TV.
State television did not show images of the drone.
On Thursday, state TV reported that the IRGC advised against any aggression against Tehran, saying that the downing of the drone carried a "clear message" to the US.
"The downing of the American drone was a clear message to America ... our borders are Iran's red line and we will react strongly against any aggression ... Iran is not seeking war with any country, but we are fully prepared to defend Iran," said commander-in-chief Hossein Salami.
The incident comes at a time of heightened tensions between Iran and the US.
The US has accused Iran of being behind a series of operations against oil tankers in highly sensitive Gulf waters.
Tehran has denied involvement.
Hormozgan borders the Strait of Hormuz, where the tanker attacks took place.
The relationship between Tehran and Washington has been particularly strained since the US last year withdrew from the 2015 nuclear deal and reimposed sanctions on Iran.
But Tehran's top security official said Wednesday there was no reason to worry about a conflict breaking out.
"There will be no war [between Iran and the US] since there is no reason for a war," said rear admiral Ali Shamkhani, secretary of Iran's Supreme National Security Council.