US President Donald Trump condemned Iran's shootdown on Thursday of a US military surveillance drone in what Washington said was international airspace.
"Iran made a very big mistake!" Trump said in a Twitter post.
Asked how the United States will respond to Iran, Trump told reporters, "You'll find out."
He reiterated that Iran's move was a big mistake in remarks to reporters before a meeting with Canadian Prime Minister Justin Trudeau, but kept open the possibility of talks with Iran.
Trump told reporters in the Oval Office that the drone was unarmed and clearly in international waters and that it could have been shot down by someone who was "loose and stupid."
"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," Trump said.
Iran’s Revolutionary Guard Corps said the "US-made Global Hawk surveillance drone" was hit with a missile "after violating Iranian air space" over the waters of Hormozgan province.
The Pentagon confirmed a US surveillance drone was shot down by Iranian forces, but it insisted the unmanned aircraft was in international airspace.
The US military's Central Command called it an "unprovoked attack."
The CENTCOM statement said the RQ-4A Global Hawk maritime surveillance drone was shot down by an Iranian surface-to-air missile while in international airspace over the Strait of Hormuz.
The incident comes at a time of growing tension between Iran and the United States following two waves of still unexplained attacks on Gulf shipping, which Washington has blamed on Tehran.
US House of Representatives Speaker Nancy Pelosi said on Thursday the United States has no appetite to go to war with Iran.
Pelosi, the top Democrat in Congress, told reporters at a regular news briefing that 20 lawmakers will receive a briefing on the "dangerous situation" in Iran.
