Iranian forces shot down a US drone over the Strait of Hormuz late Wednesday evening, according to US Central Command.

President Donald Trump's first response to the incident was a short, ominous tweet that simply said that Iran had made a "very big mistake."

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President Donald Trump tweeted on Thursday that Iran made a "very big mistake" when its forces shot down a US drone.

The Iranian Revolutionary Guard Corps shot down a US Navy Broad Area Maritime Surveillance (BAMS-D) aircraft, specifically a RQ-4A Global Hawk High-Altitude Long Endurance (HALE) drone that costs $123 million and was designed to be largely invulnerable to attack.

Read more: Iran just shot down one of the US military's most advanced drones — it costs more than an F-35 stealth fighter

The tweet comes as more and more US firepower moves into US Central Command to confront Iran, and after warnings the US has made against Iran. Many experts believe the US and Iran are on a collision course as tensions rise.

Secretary of State Mike Pompeo has been quietly warning the Iranians for more than a month that the death of even a single American service member would trigger a military counterattack. But Gen. Paul Selva, vice chairman of the Joint Chiefs of Staff, suggested earlier this week that there are other possible triggers.

Read more: The US has been privately telling Tehran that it will attack if Iran makes this one wrong move

"If the Iranians come after US citizens, US assets, or US military, we reserve the right to respond with a military action, and they need to know that," Selva told reporters. "The Iranians believe that we won't respond, and that's why we've been very clear in our message."

As US assets began moving into the Middle East early last month, White House national-security adviser John Bolton warned that "any attack on United States interests or on those of our allies will be met with unrelenting force."

It remains to be seen how the US will respond to the latest incident, which follows a string of attacks on commercial shipping and an attempted shoot-down of another US drone last week.