WASHINGTON — President Donald Trump tweeted Thursday that Iran made a "very big mistake" by shooting down a U.S. spy drone in the already tense oil-rich region.

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Hours earlier, U.S. officials said an Iranian surface-to-air missile shot down the unmanned military surveillance drone over the Strait of Hormuz. Iran said the aircraft was over its territory.

"Iranian reports that the aircraft was over Iran are false," the U.S. Central Command said in a statement. "This was an unprovoked attack on a U.S. surveillance asset in international airspace."

The U.S. benchmark West Texas Intermediate surged more than 5%, to $56.59 a barrel, while Brent crude jumped 4% on the news. Gold hit a high of $1,397.70, its highest level since Sept. 5, 2013, when it last traded at $1,400.

The downing was first announced by Iran's Islamic Revolutionary Guards on its website, Sepah News. The Iranian outlet claimed the Revolutionary Guards had shot down a U.S. "spy drone" over the southern province of Hormozgan.