Iranian forces shot down a US surveillance drone Wednesday evening, escalating an already tense situation between Washington and Tehran, Iran's capital.

The drone was a US Navy Broad Area Maritime Surveillance (BAMS-D) aircraft — a RQ-4A Global Hawk high-altitude long endurance (HALE) drone.

This high-value aircraft is one of the US military's most advanced unmanned aerial systems, and it has a price tag much higher than that of an F-35A Lightning II Joint Strike Fighter.

Iran claims the drone had entered Iranian airspace, but the US says it was shot down in international airspace over the Strait of Hormuz.

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Iranian forces took out a US unmanned aerial vehicle Wednesday evening with a surface-to-air missile, US Central Command confirmed. The drone the Islamic Revolutionary Guard Corps (IRGC) shot out of the sky happens to be one of the US military's most advanced high-altitude unmanned aircraft.

The Iranians shot down a US Navy Broad Area Maritime Surveillance (BAMS-D) intelligence, surveillance, and reconnaissance aircraft, specifically a RQ-4A Global Hawk high-altitude, long-endurance (HALE) drone, which the military uses to conduct recon operations over oceans and coastal waterways, among other areas.

The US military called the incident "an unprovoked attack on a US surveillance asset in international airspace" over the Strait of Hormuz, the entrance to the Persian Gulf. The Iranians have accused the US drone of entering Iranian airspace, an allegation Central Command characterized as completely false.

The RQ-4, which informed the development of the newer MQ-4C drones, is one of the most advanced high-altitude drones being employed operationally, The War Zone said. These aircraft, Northrop Grumman aircraft that have been used extensively in the Persian Gulf, rely on a suite of high-end electronic sensors and other intelligence-gathering systems to peer into other countries.

The aircraft, which is used by both the US Air Force and the US Navy, has a price tag higher than the US military's new F-35 stealth fighters. A Global Hawk has a unit cost of roughly $123 million, while an F-35A Lightning II Joint Strike Fighter costs only $89 million.

"This isn't a throwaway drone whose loss the US will just shrug off," Ulrike Franke, a drone expert with the European Council on Foreign Relations, said on Twitter. But it's not just the price tag that makes the loss of this drone a big deal. The drone is designed to be harder to hit, she said, because they fly at altitudes beyond the reach of some air defense defense systems.

"The RQ-4 flies at upwards of 65,000 feet," Tyler Rogoway, the editor of The War Zone, wrote. "So this would have been a sophisticated radar-guided surface-to-air missile that shot the aircraft down, not a shoulder-fired, heat-seeking missile."

Iran said the IRGC shot down the US drone with an upgraded Khordad missile-defense system, which can detect and track targets 95 miles away and down them at a distance of 30 miles, Breaking Defense reported. The system can target enemy aircraft flying as high as 81,000 feet, or roughly 15 miles.

The Global Hawk does not have any stealth capabilities or high-end countermeasures for penetration missions, leaving it vulnerable to any air defense systems that can hit high-altitude targets.

The latest incident comes just days after the crew of an Iranian boat fired an SA-7 surface-to-air missile at a MQ-9 Reaper drone, a roughly $15 million drone, but missed. Wednesday's shoot-down marks a serious escalation in tensions between the US and Iran.

Read more: An Iranian boat reportedly fired a missile at a US drone right before the tanker attack

"If the Iranians come after US citizens, US assets or [the] US military, we reserve the right to respond with a military action, and they need to know that," Gen. Paul Selva, the vice chairman of the Joint Chiefs of Staff, told reporters earlier this week.