KUWAIT CITY — In the weeks since an American drone strike killed Iranian Maj. Gen. Qasem Soleimani, U.S. military leaders have been sprinting to confront a dangerous new reality in the Middle East.

From Saudi Arabia, where troops are setting up the first U.S. presence in more than a decade; to Syria, where small teams of Americans operate near Iranian-linked forces; to Afghanistan, where officials have detected an increase in Iranian aid to the Taliban, the military is bracing for a potentially catastrophic escalation.

In visits to seven countries over the past six weeks, the top U.S. commander for the region, Gen. Kenneth "Frank" McKenzie Jr., cautioned American troops that the ballistic missile strike Iran launched days after Soleimani's death in Baghdad on Jan. 3 was unlikely the final salvo following Iran's loss of a peerless military figure.

"They're under greater pressure, and entities under great pressure can react very aggressively," McKenzie told sailors in the Arabian Sea.

Officials say Iran and its proxies have used rockets and mortars in a resumption of smaller-scale attacks on U.S. and allied targets since Soleimani's death and, in a previously unreported development, what American officials believe was a modified Russian SA-6 surface-to-air missile to shoot down a Saudi aircraft over Yemen on Feb. 14.

Saudi officials earlier this past week also announced they had disrupted an attempted attack on an oil tanker off Yemen using remote-controlled explosive boats, recalling earlier incidents the kingdom has blamed on Iranian-linked Houthi rebels.

What Iran's long-term response will be, and how President Trump might answer, are some of the unknowns military leaders must contend with in the months ahead.

A possible acceleration of Iran's long effort to end the U.S. presence in the Middle East is one reason military leaders are racing to put new protections in place for American troops, now seen at greater risk, as they watch for signs of changed Iranian behavior.

Soleimani’s death “was such a shock, so outrageous and such a break from past American behavior that Iran has basically decided it needs the U.S. out, and needs them out in real time,” said Kenneth Pollack, a scholar at the American Enterprise Institute. “It’s just too dangerous for Iran to live next door to Donald Trump.”

About 80,000 U.S. service members are deployed across the U.S. Central Command’s area of control, 20,000 more than when U.S. officials say a string of Iranian provocations against the United States and its allies began last spring.

The Pentagon has placed additional missile defense systems in countries including Saudi Arabia and Jordan over the past year. But the exposed nature of many U.S. outposts was made clear on Jan. 8, when Tehran launched about a dozen ballistic missiles at two bases housing U.S. troops in Iraq, the first such attack on American forces since the 1991 Persian Gulf War.

U.S. commanders credited advance warning systems — along with a healthy dose of luck — for the bloodless outcome, though more than 100 service members suffered concussive injuries.

McKenzie traveled to Iraq in early February to get a firsthand look at the wreckage at the Ain al-Asad base, where charred sleeping quarters and giant impact craters were proof of the challenges military leaders must confront.

The Marine general brought years of combat experience in America’s post-2001 counterinsurgency wars — including deployments to Iraq and Afghanistan — to Centcom when he assumed command last spring.

But from his first moments at Centcom’s Tampa headquarters, he faced a different kind of challenge: a heightened threat from an important state power.

In remarks throughout the region, McKenzie repeated his belief that “deterrence is born of capability and will.” Military officials say that combination was made newly compelling by the decision to undertake a targeted killing that previous administrations had considered but dismissed as too hazardous.

That deterrence strategy is visible off the Arabian Peninsula, where an amphibious ready group, with its more than 4,000 sailors and Marines, Harrier jets and giant landing craft, is among the sea-based assets standing by in case of sudden escalation. The flotilla was diverted from a mission in the European Command as tensions with Iran soared at the end of 2019.

“We’ve brought some significant naval and Marine assets into the theater to send a signal to Iran that while we don’t seek war with you . . . we’re prepared to respond if we have to,” McKenzie told troops on the USS Bataan, then operating in the Red Sea.

Farther east, in the Arabian Sea, the aircraft carrier Harry S. Truman, with its 7,500 troops across a suite of destroyers and cruisers, likewise represents an important if potentially temporary victory for officials who had questioned whether troop reductions in the Middle East in recent years would embolden Iran.

U.S. troops are also racing to renew operations in Saudi Arabia, where officials hope that F-15 jets, along with protection from a Terminal High Altitude Area Defense (THAAD) system and Patriot missile batteries, will avert attacks like September’s assault on Saudi oil facilities. Iran has denied Saudi accusations that it was responsible for those attacks.

Officials also see value in placing additional military assets west of existing air hubs in Qatar and the United Arab Emirates, which lie across the Persian Gulf from Iran. Those bases, McKenzie told troops at Saudi Arabia’s sprawling Prince Sultan Air Base, “have the virtue of being close, but also the danger of being close.”

Whether that kind of deterrence will work against a nation that has supported a range of proxy groups that have carried out strikes is an open question.

“The Iranians don’t necessarily understand our muscle movements in the way we envision they do,” said Ilan Goldenberg, a scholar at the Center for a New American Security.

Military officials in the region must also grapple with uncertainty about how long Pentagon leaders will allow them to retain the assets they see as important deterrents, including standby troops, Patriots and the carrier strike group, all of which are equally desired in the department’s planned shift to focusing on Asia.

In late February, hundreds of rapid-response troops from the 82nd Airborne Division, who were sent to Kuwait in January amid threats to Americans in Iraq, returned to Fort Bragg, N.C.

U.S. officials say Iran’s leadership is still processing the effect of Soleimani’s death and the accidental shoot-down of a commercial airliner that happened during its retaliation.

Officials suspect Tehran may bide its time, potentially taking months or years to plan what could manifest in additional attacks or, possibly, an attempt to target a senior military leader. Iran has already officially designated Centcom a terrorist organization, and the Trump administration continues to impose punishing sanctions under its “maximum pressure” campaign, increasing the strain on officials in Iran.

U.S. officials see Soleimani’s successor, Ismail Qaani, as a less potent substitute for the man credited with engineering the expansion of Iran’s influence by overseeing armed groups from Lebanon to Iraq, where militiamen are blamed for the deaths of hundreds of U.S. troops.

In the post-Soleimani era, officials regard Iraq as the most hazardous location for American troops, given their proximity to those militias and Iraqi anger about the death of Abu Mahdi al-Muhandis, a militia leader who was killed alongside Soleimani.

They hope to secure Baghdad’s permission to place Patriot batteries in Iraq, but those systems have limited range and will provide incomplete protection. U.S. facilities in the country have been targeted in repeated rocket or mortar attacks since the Dec. 27 strike that killed a U.S. contractor and kicked off the dramatic events of the past two months. U.S. officials say more American bloodshed is a virtual certainty.

They also worry about Iranian-linked fighters in Syria, where an American force of less than 1,000 is arrayed on small, exposed bases across the country’s oil-producing east. Iranian-affiliated militiamen are located in areas adjacent to U.S. outposts, west of Deir al-Zour and Bukamal, and just outside an American exclusion zone around the Tanf garrison. Last month, a U.S. partner force in Syria reported clashes with Iranian-linked militiamen.

In Green Village, where about 250 U.S. troops live amid abandoned Syrian oil villas, McKenzie relayed how the new reality could affect troops and the mission against the Islamic State — as it did in the days immediately after Soleimani’s death, when anti-extremism operations ground to a near-halt.

Speaking to troops, mostly special operators who work with local forces to hunt down Islamic State holdouts, he said his biggest concern in the near term was not a direct Iranian attack. “It’s their proxies in areas like Iraq and Syria where they could come against us,” he said.

Officials also see increased vulnerability in Afghanistan, where thousands of Americans are clustered around the capital, Kabul, and on smaller bases throughout the country without major missile defense assets.

Secretary of State Mike Pompeo linked Iran to a 2019 bombing in Kabul, but officials have primarily accused Iran of providing small arms and some funding to the Taliban, making Tehran a secondary player in Afghanistan’s long conflict.

McKenzie suggested that could change under the leadership of Qaani, who served as point man in Afghanistan for Iran’s elite Quds Force. Speaking in Kabul, the American general said there were indications of Iran’s increased “malign activity” in Afghanistan, but he declined to provide details.

Perhaps the biggest challenge for military officials will be ensuring that any additional Iranian attacks do not escalate into a major regional conflagration.

That involves high-stakes analysis of how Iran might respond to U.S. counterstrikes — suggesting the Pentagon might argue for narrowly targeted reprisals — and calculations about what political leaders, including Trump, would demand in such a scenario.

Speaking to fighter pilots aboard the USS Harry S. Truman, McKenzie said that he didn’t know how any escalation would begin but that he was confident about how it would conclude.

“That’s going to end in the defeat of Iran,” he said. “But that won’t be good for Iran and won’t be good for the region.”

Paul Sonne in Washington contributed to this report.