“General Soleimani was actively developing plans to attack American diplomats and service members in Iraq and throughout the region,” it added, blaming him for recent attacks on U.S. troops and the U.S. Embassy in Baghdad. “This strike was aimed at deterring future Iranian attack plans.”

Iran’s foreign minister, Javad Zarif, accused the U.S. of “international terrorism” and said it “bears responsibility for all consequences of its rogue adventurism.”

Qassem Soleimani. | Ebrahim Noroozi/AP Photo

Even the possibility that the U.S. had directly targeted Soleimani – especially on Iraqi soil – sent shockwaves around the globe, spiking oil prices and leading to instant assessments of the potential fallout. U.S. officials have long depicted Soleimani as a paramilitary and terrorist mastermind, deemed responsible for attacks on American troops in Iraq and against U.S. interests all over the world.

“It is hard to overstate the significance,” said retired Gen. David Petraeus, who oversaw the “surge” of American troops in Iraq in the violent years after the 2003 U.S. invasion. “But there will be responses in Iraq and likely Syria and the region.”

Some current and former U.S. officials, as well as veteran Iran observers, said the killing was an escalatory move far beyond what they had ever expected.

“There’s no chance in hell Iran won’t respond,” said Afshon Ostovar, an expert on Soleimani and author of “Vanguard of the Imam” a book about Iran’s Islamic Revolutionary Guard Corps.

The strike also reportedly killed Iraqi militia commander Abu Mahdi al-Muhandis, who was traveling in the same convoy as Soleimani. It astonished even some members of the Trump administration who said killing the Iranian general had not been seriously considered — at least not recently.

“I can’t believe it,” one U.S. official said. “The immediate concern for me is: What’s the next step from Iran? Is this the beginning of a regional conflagration?”

A former U.S. official who dealt with the Middle East said the strike was especially notable because it targeted the leader of a state apparatus, as opposed to a non-state actor.

“We need to be prepared that we’re now at war,” he said.

A Middle Eastern official said that a retaliation by Iran – known for its own assassinations abroad – could occur anywhere.

Supreme Leader Ayatollah Ali Khamenei, left, Iraqi Shiite cleric Muqtada al-Sadr, center, and commander of Iran's Quds Force, Qassim Soleimani. | Office of the Iranian Supreme Leader via AP

“It could be targets in Africa, it could be in Latin America, it could be in the Gulf, it could be anything,” the official said. “I don’t think they’re going to take the assassination of one of their key guys and just turn the other cheek.”

Soleimani had been leading the Quds Force, a unit of Iran’s Islamic Revolutionary Guard Corps that is behind much of Iran’s military actions outside its borders. He was a hugely popular figure in Iran, and a frequent rhetorical target of President Donald Trump and his aides.

Secretary of State Mike Pompeo, for instance, repeatedly singled out Soleimani for criticism as part of the Trump team’s broader anti-Iran “maximum pressure” campaign. Part of that campaign included designating the IRGC as a foreign terrorist organization.

Trump’s “maximum pressure” campaign has intensified in recent months, as the U.S. has clashed with Iran and its proxies. Just days ago, an American contractor died in Iraq after an attack by an Iraqi militia allied with Iran. The U.S. responded by bombing sites held by the group, killing some two dozen militiamen.

Within days, protesters believed to be linked to the Iran-backed militia breached parts of the U.S. Embassy compound in Baghdad. The Iraqi government, meanwhile, condemned the U.S. airstrikes, noting that the militia had ties to its own security forces.

In comments Thursday that may have foreshadowed the strike, Esper warned that the U.S. reserved the right to strike preemptively in Iraq or the region. “If we get word of attacks, we will take preemptive action as well to protect American forces, protect American lives,” the defense secretary told reporters at the Pentagon. “The game has changed.”

But the killing of Soleimani was a shocking development, even considering how tense U.S.-Iran relations have grown under Trump. The president has heaped economic sanctions on Iran’s Islamist regime and at times threatened Tehran with military action.

Trump also pulled the United States out of the internationally negotiated nuclear deal with Iran, saying it was too narrow and should have curbed Iran’s non-nuclear aggressions in the region as well as its nuclear program.

The two countries nearly came to a direct military clash earlier this year after Iran was blamed in a string of attacks on international oil tankers. The U.S. and Iran even downed each other’s drones, but Trump backed down at the last minute from staging a military strike directly on Iran.

Though he has sent thousands more troops to the region, Trump has said repeatedly that he doesn’t want to engage in a new war in the Middle East. But the possibility that Iran will feel compelled to respond with escalatory actions of its own could embroil the president in a politically risky confrontation in the middle of an election year.

Democrats reacted cautiously to Soleimani’s killing, but immediately raised questions about its legality, even as Republicans hailed it as an unalloyed triumph.

“Soleimani was an enemy of the United States. That’s not a question,” tweeted Sen. Chris Murphy (D-Conn.). "The question is this – as reports suggest, did America just assassinate, without any congressional authorization, the second most powerful person in Iran, knowingly setting off a potential massive regional war?”

Former vice president Joe Biden, the Democrats' leading presidential candidate, said that while 'no American will mourn Qassem Soleimani’s passing," his killing was a "hugely escalatory move" that would prompt Iranian reprisals. "President Trump just tossed a stick of dynamite into a tinderbox.”

The death of Soleimani is likely to have deep implications in Iraq and other countries in the region, where Iran has powerful political allies and proxy forces.

PHOTOS: The world reacts to Qassem Soleimani's death | Vahid Salemi/AP Photo

The most immediate repercussions will be felt in Iraq, which for years has been a battleground for influence between Washington and Tehran. Iran has long sought to push U.S. troops out of Iraq, where they’ve maintained a presence since the 2003 invasion that toppled dictator Saddam Hussein.

Many Iraqis are sick of Iranian influence in their country. Recent widespread demonstrations have featured chants against Tehran and the Shiite clerics who largely run its religion-infused regime.

But Iraq also wants to avoid becoming ground zero for a U.S.-Iran war, while keeping up friendly relations with Iran to help its own economy.

“It is only fair for Iraq to strive to achieve this balance but given the ‘beef’ between Iran and the U.S. it’s a lost effort,” a former Iraqi diplomat told POLITICO. The “Trump administration is on a zero-sum mission vis a vis Iran, and expects Iraq to pick one side only.”

Trump’s hard line toward Iran has earned applause from other Middle Eastern countries, notably Israel, Saudi Arabia and the United Arab Emirates, which consider Iran an implacable enemy bent on manipulating the region in its favor.

Still, Saudi and UAE diplomats in recent months have tried to cool tensions with Iran. And while they’re likely to shed few tears for Soleimani, they may worry about the blowback Iran and its allies are capable of creating in their own countries.

The Pentagon had considered striking Soleimani before, during the height of U.S. involvement in Iraq, when the Quds Force was supplying bombs and other weapons to Iraqi Shiite militia groups that the military estimated killed over 600 U.S. troops.

In 2006, according to an Army study of the Iraq War that was eventually declassified, the U.S. military headquarters in Iraq “prepared a plan to kill or capture Qods Force commander Qassem Soleimani, who had made his way into Iraq for at least the second time” that year, the next time he visited the country.

But U.S. commanders “ultimately refrained from taking action against Soleimani, allowing the Iranian general to enter and exit Iraq unhindered,” says the study. It does not explain why the military did not act on the proposal or whether it was considered at higher levels, such as at the military’s Central Command or the Pentagon.

U.S. commandos in Iraq did detain some of Soleimani’s Quds Force associates during raids later in 2006 and 2007, though, after the Bush administration granted expanded authorities for the elite troops to go after Iranian targets in the country.

Those captures proved controversial with the Iraqi government, which often granted Quds Force members diplomatic immunity and insisted on their release.

While Soleimani’s death is no doubt a major loss for the Iranian regime, it is unlikely the ruling clerics and their military aides were entirely unprepared for it.

Ostovar, the Soleimani and IRGC expert, said in all likelihood Iran will name a successor soon because its systematic approach to their rule is “really strong.”

“He was really just sort of the forward or outside face of the Islamic Republic,” Ostovar said. “He was the face of their strategy, but their strategy goes beyond him.”

