U.S.-Iranian tensions heightened Thursday when Iran's Revolutionary Guard shot down a U.S. surveillance drone, a bold strike that drew a stern warning from President Donald Trump and prompted top Pentagon officials to formulate military response options.

Iran said the drone was destroyed over its coast and said the incident sent a "clear message" that the Persian Gulf nation was ready to defend itself from what it views as Western aggression. The Pentagon, however, said the incident played out in international waters over the Strait of Hormuz.

Trump told reporters he found it "hard to believe" that the drone was shot down intentionally, saying more likely a lower-level officer was responsible without approval of superiors.

"Iran made a very big mistake," President Trump said, adding that "you'll soon find out" if the U.S. will retaliate.

The two countries have escalated their rhetoric since two oil tankers were attacked in the Gulf of Oman last week. The United States blames Iran for the attacks; Tehran denies responsibility.

U.S. Central Command said the Navy Broad Area Maritime Surveillance ISR aircraft was shot down by an Iranian surface-to-air missile system. The Pentagon released a short, grainy video clip it said showed the smoke trail of the drone seconds after it was hit.

"Iranian reports that the aircraft was over Iran are false," said Navy Capt. Bill Urban, spokesman for U.S. Central Command. He called the strike an "unprovoked attack on a U.S. surveillance asset."

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Lt. Gen. Joseph Guastella, commander of U.S. Air Forces Central Command in Qatar, said the drone was attacked about 20 miles from Iran. "This attack is an attempt to disrupt our ability to monitor the area following recent threats to international shipping and free flow of commerce," he said.

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Senior Pentagon officials consider the incident a serious provocation and are considering military options to respond to it, according to a Defense official with knowledge of the discussions but who is not authorized to speak publicly about them. One response could be to strike the missile battery that launched the attack.

Revolutionary Guard Commander Major General Hossein Salami said Iran does not want war, but that the incident should serve as a warning to the U.S. to stay away.

“The downing of the U.S. drone had an explicit, decisive and clear message that defenders of the Islamic Iran’s borders will show decisive and knockout reactions to aggression against this territory,” Salami said at a news conference in Kurdistan Province. “Borders are our red line, and any enemy violating these borders will not go back."

The RQ-4 Global Hawk, built by defense giant Northrop Grumman, is a high-altitude drone capable of flying for more than 30 hours at a time. It is not the drone you see your neighbor flying over your street – this one is more than 47 feet long and has a wingspan of more than 131 feet. The military has flown them since 2001.

Robert Pape, director of the Project on Security and Threats at the University of Chicago, said the drone was probably probing and testing Iranian air defenses. The incident likely provided the U.S. military with information that could be used if Trump decides to attempt airstrikes at Iranian nuclear installations or other targets, he told USA TODAY.

“You probably don’t expect it (the drone) to be shot down, but you are expecting that it would light up the air defenses,” he said. “And I’m sure the incident provided valuable tactical information.”

The Iranian Guard said the drone was shot down by its air force and its Third of Khordad air defense system. The guard said the drone fell in the Kouh-e Mobarak region in the Central district of Jask, about 750 miles southeast of Tehran, after the aircraft violated Iran's airspace.

The U.S. military previously accused Iran of firing a missile at another drone last week that was responding to the attack on the oil tankers. In recent weeks the U.S. has sent an aircraft carrier to the Mideast and deployed additional troops to join tens of thousands already in the region.

James Piazza, a Penn State political science professor specializing in the Islamic world, said it wasn't clear what Iran hoped to gain by destroying the drone.

"Iran very well may think that the U.S. will continue to ramp up its belligerence," Piazza told USA TODAY. "They may be trying to show the U.S. that if the U.S. opts for military action, Iran is able to make things costly and ugly."

Relations between the U.S. and Iran have been steadily deteriorating since Trump pulled the U.S. out of a global nuclear deal with Tehran a year ago. The administration brought back sanctions on banking, oil and petrochemicals.

Other nations sought to keep the nuclear deal in place, and Iran was slow to formally bow out. However, this week Iran's nuclear agency warned the country was 10 days away from breaking the uranium stockpile limit set under the agreement.

Sina Toossi, research associate at the National Iranian American Council, a Washington-based nonprofit supporting human rights and democracy for Iran, said Iran must be condemned by the international community if it is proved that the drone was shot down over international waters. But Toossi also accused John Bolton, Trump's national security adviser, of provoking Iran-U.S. tensions.

"There are no military solutions to the U.S. disputes with Iran, only diplomatic ones," Toossi said. "However, rather than pursue sincere diplomacy, President Trump has elected to pile on pressure with no strategic foresight at the behest of uber-hawkish advisers like John Bolton."

Contributing: Tom Vanden Brook, David Jackson and Donovan Slack

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