Top administration officials and lawmakers have left the White House after a classified briefing lasting over an hour, about Iran’s sudden downing of an American surveillance drone in the Middle East — and a “measured” U.S. response, they suggested, is likely coming soon.

Amid mounting tension between the U.S. and Iran, the White House earlier Thursday invited House and Senate leaders and Democrats and Republicans on the House and Senate Intelligence and Armed Services Committees to meet with President Trump in the White House’s secure Situation Room.

Others who arrived for the meeting included CIA Director Gina Haspel, Chairman of the Joint Chiefs of Staff Gen. Joseph Dunford, Secretary of State Mike Pompeo, acting Defense Secretary Patrick Shanahan and Army Secretary Mark Esper, whom Trump has said he’ll nominate as defense secretary.

Shanahan was spotted outside the White House carrying a folder stamped “SECRET/NOFORN,” an intelligence classification category prohibiting distribution to anyone outside the government.

Senate Majority Leader Mitch McConnell, R-Ky., told Fox News that “we had a good briefing” and that the Trump administration would engage in “measured responses.”

McConnell confirmed the U.S.’s firm position that the drone was operating in international airspace, even as Iran has tried to make the case that the drone had “violated” Iranian airspace.

In a statement, House Republican Leader Kevin McCarthy and Ranking Members Michael McCaul of Texas (House Foreign Affairs), Devin Nunes of California (House Intelligence), and Mac Thornberry of Texas (House Armed Services) all condemned Iran’s “direct attack,” and demanded “measured” retaliation.

“Iran directly attacked a United States asset over international waters,” the Republicans wrote. “This provocation comes a week after they attacked and destroyed two commercial tankers in international waters. There must be a measured response to these actions. President Trump and his national security team remain clear-eyed on the situation and what must be done in response to increased Iranian aggression. In Congress, we stand ready to support our men and women in uniform, our country, and our allies in the region.”

House Speaker Nancy Pelosi, D-Calif., issued a separate statement after the briefing calling for calm.

TRUMP SAYS IRAN’S US DRONE SHOOT-DOWN MAY HAVE BEEN ‘MISTAKE,’ BUT ‘COUNTRY WILL NOT STAND FOR IT’

“In light of the targeting of an unmanned U.S. drone by Iran, it is essential that we remain fully engaged with our allies, recognize that we are not dealing with a responsible adversary and do everything in our power to de-escalate.

“This is a dangerous, high-tension situation that requires a strong, smart and strategic, not reckless, approach,” Pelosi said.

Speaking to reporters, Pelosi said she also was convinced that U.S. intelligence was correct in its assessment that the drone was in international airspace when it was shot down. But, Pelosi added, the Trump administration legally would need to obtain Congress’ approval before taking military action.

“We make it very clear that to get involved in any military activities, we must have a new Authorization for Use of Military Force (AUMF),” Pelosi cautioned.

Senate Minority Leader Chuck Schumer, D-N.Y., said he told the president during the briefing that there should be a “robust, open debate,” and that Congress should “have a real say.”

He said he was worried the administration “may bumble into a war.”

“We have an amendment supported by every Democrat to the NDAA in the Senate, led by Senator Udall, which would require Congressional approval of any funding for a conflict in Iran,” Schumer said in a statement. “It’s supported by all Democrats in the Senate. We are asking leader McConnell to do the right thing and give us a vote next week on the NDAA on that amendment.”

Footage on social media also showed Schumer appearing to celebrate after the briefing, but Schumer later clarified that he was happy his mother had been released from the hospital.

Hours earlier, the Pentagon released video showing the smoke trail of a Navy drone that was shot out of the sky over the Strait of Hormuz by Iran, in what military officials described as an “unprovoked attack.”

Trump told reporters that Iran made a “very big mistake” but also said he had the feeling that it might have been the result of someone being “loose” or doing something “stupid,” rather than a deliberate provocation by Iran.

The U.S. Navy RQ-4A Global Hawk, an unmanned aircraft with a wingspan larger than that of a Boeing 737, was downed by an Iranian Islamic Revolutionary Guard Corps surface-to-air missile that was fired from near Goruk on Wednesday night, according to Lt. Gen. Joseph Guastella, head of U.S. Air Forces Central Command.

“This was an unprovoked attack on a U.S. surveillance asset that had not violated Iranian airspace at any time during its mission,” Guastella said. “This attack is an attempt to disrupt our ability to monitor the area following recent threats to international shipping and free flow of commerce.”

Guastella said at the time it was struck by the missile, the drone was operating at a “high altitude” over 20 miles from the nearest point of land on the Iranian coast.

Some Democrats, for their part, blamed Trump for the episode. Presidential candidate Joe Biden said Trump has made military conflict with Iran more likely, and that “another war in the Middle East is the last thing we need.”

“Iran directly attacked a United States asset over international waters.”

— House Republican Leader Kevin McCarthy, and Ranking GOP Members

Biden said Trump’s strategy in Iran has been “a self-inflicted disaster” since the president withdrew the U.S. from the Iran nuclear agreement negotiated when Biden served under then-President Barack Obama as vice president.

The Trump administration called that deal a reckless giveaway to a dangerous regime that only emboldened and empowered its imperialistic and terroristic ambitions. By reimposing sanctions that had been lifted under the Obama-era deal, Trump administration policies largely have crippled Iran’s economy, sending inflation above 30 percent and devastating oil revenues.

Biden asserted there’s no question Iran “continues to be a bad actor that abuses human rights and supports terrorist activities.” But, he added that the U.S. needed presidential leadership.

US NAVY DRONE SHOT DOWN BY IRANIAN MISSILE OVER STRAIT OF HORMUZ IN ‘UNPROVOKED ATTACK,’ CENTRAL COMMAND SAYS

In a video released Thursday afternoon, the smoke trail of the drone could be seen in a black-and-white video as the craft plummeted.

Guastella said the drone landed in “international waters” about 20 miles from Iran. U.S. officials told Fox News that investigators were racing to find the wreckage ahead of Iranian forces.

The U.S. Navy’s RQ-4A Global Hawk drone provides real-time intelligence, surveillance and reconnaissance missions  “over vast ocean and coastal regions,” according to the military. The drone was deployed to the Middle East in the past few days as part of reinforcements approved by Trump last month.

The high-altitude drone can fly up to 60,000 feet or 11 miles in altitude and stay aloft for 30 hours at a time. It’s used to spy on Iranian military communications and track shipping in the busy waterways. Each drone costs up to $180 million.

Also Thursday afternoon, presidential candidate Kirsten Gillibrand, D-N.Y., demanded that Trump abstain from sending American troops into a conflict with Iran without congressional approval.

In recent weeks, the U.S. has sped an aircraft carrier to the Mideast and approved sending 1,000 additional troops “to address air, naval, and ground-based threats” in the region. Mysterious attacks have targeted oil tankers as Iranian-allied Houthi rebels launched bomb-laden drones into Saudi Arabia.

The New York senator outlined her position in a sharply worded letter to the White House on Thursday.

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Gillibrand wrote she was “deeply concerned that your administration’s stepped up military presence in the Middle East, in conjunction with your dangerous and confusing rhetoric, may lead the United States into a protracted, costly, and unnecessary war with Iran. Such a war is not authorized, would unnecessarily risk the lives of Americans and our allies, cause enormous human suffering, and destabilize the economy.”

Fox News’ Travis Fedschun, Hillary Vaughn and The Associated Press contributed to this report.

U.S. military officials returned fire — verbally — hours after Iran blasted a Navy high-altitude drone out of the sky over the Strait of Hormuz, with U.S. Central Command leaders on Thursday slamming the “unprovoked” strike and Tehran’s subsequent “false” justifications for it.

The downing of the drone, via surface-to-air missile, is only the most recent Iranian provocation in the region, coming on the heels of a disputed attack on a pair of oil tankers in the Gulf of Oman last week. U.S. officials say Iran was behind the tanker attacks, however, the Islamic Republic has not claimed responsibility and even suggested American involvement in the plot.

Similarly, Iran claimed the U.S. drone on Thursday was over Iranian airspace when it was shot down — but American officials stated unequivocally the incident occurred in international airspace. U.S. Central Command said in a statement that a U.S. Navy Broad Area Maritime Surveillance ISR aircraft, known as a BAMS-D, was shot down at approximately 7:35 p.m. ET on Wednesday.

BIDEN CALLS IRAN TENSIONS ‘SELF-INFLICTED DISASTER’ AFTER US DRONE SHOOT-DOWN

In a statement read to reporters at the Pentagon Lt. Gen. Joseph Guastella, Commander, U.S. Air Forces Central Command said the drone was flying over the Gulf of Oman and the Strait of Hormuz on a surveillance mission in international airspace when it was shot down from the missile fired from a location near Goruk, Iran.

“This was an unprovoked attack on a U.S. surveillance asset that had not violated Iranian airspace at any time during its mission,” Guastella said. “This attack is an attempt to disrupt our ability to monitor the area following recent threats to international shipping and free flow of commerce.”

Guastella said at the time it was struck by the missile, the drone was operating at a “high-altitude” approximately 34 kilometers from the nearest point of land on the Iranian coast.

“This dangerous and escalatory attack was irresponsible and occurred in the vicinity of established air corridors between Dubai, UAE, and Muscat Oman, possibly endangering innocent civilians,” he said.

LINDSEY GRAHAM: IF IRAN ‘ATTACKS SHIPPING AGAIN,’ US SHOULD CONSIDER ‘TAKING OUT THEIR NAVY, OIL REFINERIES’

The U.S. Navy’s RQ-4A Global Hawk drone provides real-time intelligence, surveillance, and reconnaissance missions  “over vast ocean and coastal regions,” according to the military.

Iran also tried to shoot down another drone, but missed, U.S. officials told Fox News. Officials are now scrambling to find the wreckage in the water before Iranian forces recover it.

The Navy RQ-4A Global Hawk drone deployed to the Middle East in the past few days as part of reinforcements approved by President Trump last month.

The high-altitude drone can fly up to 60,000 feet or 11 miles in altitude and loiter for 30 hours at a time. It’s used to spy on Iranian military communications and track shipping in the busy waterways. Each drone costs up to $180 million dollars.

Besides the drone incident, U.S. officials told Fox News that Iranian-backed forces fired cruise missiles Wednesday night into Saudi Arabia, hitting a power plant. The spate of recent attacks come amid the backdrop of heightened tensions after the U.S. decision a year ago to withdraw from Tehran’s nuclear deal reimpose sanctions.

President Trump said on Twitter that Iran “made a very big mistake!” before telling reporters alongside Canadian Prime Minister Justin Trudeau the U.S. would not stand for it.

At the same time, he seemed to leave open the possibility that it was not an intentional act.

“I find it hard to believe it was intentional, and it could have been someone who was loose and stupid,” he said.

A commander for Iran’s Revolutionary Guard claimed the drone was shot down over Iranian airspace to send a “clear message” to the U.S., and marked the first direct Iranian-claimed attack of the crisis.

“We do not have any intention for war with any country, but we are fully ready for war,” Revolutionary Guard commander Gen. Hossein Salami said in a televised address.

Iran’s paramilitary Revolutionary Guard, which answers only to Supreme Leader Ayatollah Ali Khamenei, said it shot down the drone on Thursday morning — causing some confusion about the timeline of the incident — when it entered Iranian airspace near the Kouhmobarak district in southern Iran’s Hormozgan province. Kouhmobarak is some 750 miles southeast of Tehran and close to the Strait of Hormuz.

CAL THOMAS: IS WAR WITH IRAN INEVITABLE?

The Guard said it shot down the drone at 4:05 a.m. after it collected data from Iranian territory, including the southern port of Chahbahar near Iran’s border with Pakistan. Iran used its air defense system known as Third of Khordad to shoot down the drone — a truck-based missile system that can fire up to 18 miles into the sky, the semi-official Fars news agency reported.

The Guard described the drone as being launched from the southern Persian Gulf but did not elaborate. American RQ-4A Global Hawks are stationed at the Al-Dhafra Air Base in the United Arab Emirates, near the capital, Abu Dhabi.

Salami, speaking to a crowd in the western city of Sanandaj, described the American drone as “violating our national security border.”

“Borders are our red line,” Salami said. “Any enemy that violates the borders will be annihilated.”

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The U.S. said Iran fired a missile at another drone last week that responded to the attack on two oil tankers near the Gulf.

Another senior U.S. official told Fox News last week that an MQ9 Reaper drone was fired on by the Iranians shortly after it arrived at the scene where the MV Altair tanker sent out a distress signal.

After the tanker incident, Pompeo said his assessment was based on “intelligence, the weapons used, the level of expertise needed to execute the operation, recent similar Iranian attacks on shipping, and the fact that no proxy group operating in the area has the resources and proficiency to act with such a high degree of sophistication.”

Fox News’ Jennifer Griffin, Adam Shaw, Lukas Mikelionis and The Associated Press contributed to this report