WASHINGTON — U.S. forces were prepared for a retaliatory strike on Iran on Thursday, but later withdrew those plans with just hours to go, according to officials and news reports.

A U.S. official, speaking on the condition of anonymity, told the Associated Press that the military had prepared for limited strikes on Iran after the nation shot down a U.S. drone over international waters, but that approval was abruptly withdrawn.

The New York Times, citing several unnamed senior administration officials, reported that President Donald Trump approved the strikes and then stopped them. The U.S. officials had expected a strike as late as 7 p.m., the Times reported.

The decision followed a day of tensions with Iran after the country's military shot down the drone, which Iran said violated its airspace – claims the U.S. said are false. The Pentagon called the action a "dangerous and escalatory attack," and Trump labeled it a "very big mistake," suggesting a retaliatory U.S. strike was imminent.

Acting Defense Secretary Patrick Shanahan huddled Thursday with national security officials at the White House to discuss military options, including an attack on the site that launched the missile that destroyed the unmanned surveillance aircraft, according to a Defense official familiar with the discussions but not authorized to speak about them publicly.

Iran shoots down U.S. drone:Donald Trump plays down Iran attack on US drone as a 'big mistake' by someone 'stupid'

The White House on Thursday night declined the AP's requests for information about whether Trump changed his mind.

Earlier Thursday, the White House summoned leaders in Congress for a late-afternoon briefing on Iran.

"I sense that a limited, targeted reprisal strike is likely – but with the emphasis on 'limited,'" said Michael O'Hanlon, a military analyst at the Brookings Institution. "Then Iran will decide what it wants to do next. Not a huge risk of escalation. But still a non-zero risk."

In the last two years, U.S. and allied forces have mounted limited airstrikes in Syria that could offer a guide to an attack on Iran. In April 2018, American, British and French forces fired 105 missiles on three Syrian chemical weapons facilities a week after the regime of Bashar al Assad had launched a brutal attack that killed 40 civilians. A year earlier, Tomahawk cruise missiles struck an airfield in Syria where Pentagon officials said a chemical attack had originated.

Trump responds:'You'll soon find out' if US retaliates after Iran shoots down drone, Trump warns

In recent weeks, the Pentagon has shifted an aircraft carrier strike group, B-52 bombers and thousands of troops to the region to confront Iran and protect American forces in the region. The bombers offer the option of launching long-range cruise missiles far from Iran's air defenses.

The Navy RQ-4 was flying in international airspace over waters where two tankers were attacked in recent weeks when it was blasted by a surface-to-air missile fired from a battery near Goruk, Iran, according to Air Force Lt. Gen. Joseph Guastella, commander of Air Force assets in the Middle East. Iran has denied attacking the tankers, and said Thursday that the drone had violated its airspace.

"This dangerous and escalatory attack was irresponsible and occurred in the vicinity of established air corridors between Dubai, United Arab Emirates, and Muscat Oman, possibly endangering innocent civilians," Guastella said.

Experts had predicted Iran would continue acting out before the drone strike and that the crisis could spiral. Earlier this week, Philip Gordon, a negotiator on the deal to keep Iran from developing a nuclear weapons, said there were “not a lot of good options and a significant risk of escalation.”

Gordon, who was White House coordinator for the Middle East, North Africa and the Gulf Region under President Obama from 2013 to 2015, pointed to the Trump administration declaring Iran’s Revolutionary Guard a terrorist organization in April, and then imposing sanctions on other countries buying Iranian oil, which “severely punished the Iranian economy.”

Iran v. U.S.:What Iran and the United States are saying about the shooting down of the U.S. drone

The tensions:Escalating Iran crisis looks a lot like the path US took to Iraq war

“I think that’s what brought us to the crisis that we’re in now,” Gordon, now senior fellow in U.S. foreign policy at the Council on Foreign Relations, said he believes Iran is responsible for the recent sabotaging of ships and explosions in the Gulf, and he noted the regime “ominously” has vowed to restart its nuclear program. He said he didn’t see many off-ramps from imminent military conflict.

“There was… the notion that by squeezing the Iranians so hard the people would rise up and push the regime aside,” Gordon said. “That doesn’t seem to be happening anytime soon.”

Gil Barndollar, a former Marine and senior fellow at non-interventionist-leaning think tank Defense Priorities, said Thursday that “it would be hard to bet against” United States taking military action, even in a limited way, in response to the drone strike. But he hopes the Trump administration uses the incident as “an opportunity” to restart diplomatic efforts.

“I would hope we use this opportunity to steer back toward negotiations and look at re-orienting things with Iran on a live-and-let-live basis,” said Barndollar, who is also the director of Mideast studies at the Center for the National Interest.

Contributing: The Associated Press