The US President has warned that Iran "made a very big mistake" in shooting down a US military surveillance drone.
Donald Trump issued the warning as both country's dispute the circumstances surrounding the incident.
Tehran insists the aircraft was shot down after it entered Iranian airspace near the Kouhmobarak district in the southern Hormozgan province.
The US Military Central Command said the drone was downed in international airspace over the Strait of Hormuz, south of Iran.
The statement added that "Iranian reports that the aircraft was over Iran are false" and that "this was an unprovoked attack on a US surveillance asset in international airspace."
In a statement quoted by state media, Iran's Islamic Revolutionary Guard Corps (IRGC) said the drone was a RQ-4 Global Hawk - an aircraft equipped with high-resolution surveillance equipment.
IRGC chief commander Hossein Salami said the downing of the drone was a 'clear message'.
He observed: "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."
Tensions are running high in the region after the US accused Iran of attacking oil tankers last week.
Iran has denied any involvement in the attacks in the Gulf of Oman.
The US has already said it is sending an additional 1,000 troops to the Middle East in response to alleged 'hostile behaviour' by Iran.