The stunning killing of Iran’s top military commander by a US drone strike has taken out the longtime architect of anti-American violence in the Middle East. But the attack opened a Pandora’s box of geopolitical peril that could threaten the United States for years, security analysts, former diplomats, and combat veterans said Friday.

Qassem Soleimani, the mastermind of Iran’s destabilizing military strategy from Iraq to Lebanon to Yemen, was responsible for killing more than 600 American service members and civilians over three decades, US officials have said.

But his death Thursday night at Baghdad Airport in neighboring Iraq suddenly pushed a long-simmering confrontation with Iran toward yet another war in the Middle East, the analysts said. Whether the Trump administration has planned adequately for the aftermath of such a dramatic escalation in hostilities is far from clear, they added.

“I wouldn’t even pretend to guess how events will unfold from here,’’ said Andrew Bacevich, a retired Army colonel who lives in Walpole. “History is full of examples of how wars begin through inadvertence. Events take charge. We are in one of those moments where something like that could happen.’’

“The big picture is this: That the global war on terrorism that began after 9/11 is going to continue,’’ added Bacevich, who also taught at Boston University.

Secretary of State Mike Pompeo said the strike was ordered after Soleimani appeared close to launching a fresh round of attacks against Americans and US interests in the region.

Former US ambassador Nicholas Burns, a professor at the Kennedy School of Government at Harvard University, said that if the Trump administration “believed further attacks on our embassies in Iraq and the region were imminent, it had a legitimate reason to attack Soleimani.’’

“We should have no sympathy for him,’’ Burns said. "He was the major force for terrorism in the Middle East.’’

However, the killing is likely to inflame hostilities across the region and lead to demands for proof of intended Iranian assaults, he said.

President Trump “needs to protect our diplomats and military personnel from Iranian counterattacks,’’ said Burns, a former undersecretary of state. “He needs to line up allied support. He needs to reveal publicly specific information that will support the US claim that further attacks were imminent. Did he think of all this before launching the drone strike?’’

Samantha Power, a Kennedy School professor who served as US ambassador to the United Nations under former president Barack Obama, suggested via Twitter that Trump will have difficulty justifying the killing to the world.

“This is where having credibility — and having a president who didn’t lie about everything — would be really, really helpful,’’ Power wrote.

Power also chided Trump for tweeting an image of the US flag following the airstrike. “A flag is not a strategy,’’ she wrote.

Representative Seth Moulton, a Democrat from Salem, expressed grave doubts about whether the administration has planned for the treacherous road ahead.

“We have no idea what comes next. Iran will retaliate, and this absolutely could lead to a regional war. The administration is violating its own stated policy in Iran and the broader Middle East,’’ said Moulton, a four-tour Marine veteran of Iraq.

That policy — to deter regional aggression, stop the Iranian nuclear weapons program, and bring Iran to the negotiating table — are all undercut by this strike, which was ordered without consulting Congress, Moulton said.

“I’ve asked them repeatedly for their plans, their strategy with Iran, as a member of the House Armed Services Committee. They can never answer basic questions,’’ Moulton said. “Almost nothing they have said or done to date makes sense.’’

Iran’s supreme leader, Ayatollah Ali Khamenei, pledged to avenge Soleimani’s death. Where, when, and how that will occur is pure speculation, but analysts said retaliation is sure to come.

The most immediate danger appears to be for US diplomatic and military installations in the Middle East. Following the two-day siege of the heavily fortified US Embassy in Baghdad this week, a move that Soleimani is believed to have authorized, any US presence in the region is a potential target.

The embassy assault followed American airstrikes against Iranian-backed militia members in Iraq, which were preceded by a Dec. 27 rocket attack that killed an American contractor on an Iraqi base.

Soleimani’s killing, however, is the most successfully aggressive US move against Iran since the Islamic revolution deposed that country’s shah in 1979.

Maura Sullivan of Portsmouth, N.H., a Marine veteran of Iraq and former senior Pentagon official, echoed other analysts who said the two countries are entering a perilous and uncharted future.

Soleimani’s death, “while not unwarranted, raises grave concerns about the security of American personnel in the Middle East and southeast Asia and is a significant step toward a possible war, particularly given when and how it was conducted,’’ Sullivan said.

The United States has not targeted and killed a senior military leader of another country since World War II, when it downed a plane in 1943 that carried Admiral Isoroku Yamamoto, who masterminded the Japanese surprise attack on Pearl Harbor.

Some analysts praised the strike, including Michael Doran, a senior fellow at the Hudson Institute who served on the National Security Council under former president George W. Bush.

“Qassem Soleimani’s hands are drenched in American blood, and in the blood of Middle Easterners,’’ Doran tweeted Friday. “The disproportionate response was what he got under previous administrations: a free pass to kill. What he got last night was justice.’’

In the weeks and months ahead, the Trump administration will be judged on whether it has a follow-up strategy, or whether Soleimani’s death was an isolated reaction to Iranian-backed violence, many said.

“The ball is in Tehran’s court. I would be surprised if they allowed this to happen without a violent response and tailor that response in a way that will make the decision-making within the US national security establishment more complicated,’’ said Bacevich, president of the Quincy Institute for Responsible Statecraft, a Washington, D.C., think tank.

“They’re not stupid. They will find a way to respond that will not present a clear retaliatory path for the United States,’’ he added.

Burns, the former ambassador, said the United States does not appear well prepared to manage such a complex crisis.

“Trump is surrounded by sycophants, having fired those who’ve dissented,’’ Burns said. “He has purged Iran specialists. He has abolished [National Security Council] processes to review contingencies. He is seen as a liar around the world.

“This is likely to get very ugly, very quickly.’’

Brian MacQuarrie can be reached at brian.macquarrie @globe.com. Travis Andersen can be reached at travis.andersen@globe.comFollow him on Twitter @TAGlobe.