WASHINGTON — Gulf Arab states are on edge after President Donald Trump's decision to kill top Iranian commander Gen. Qassem Soleimani, fearing tensions between the United States and Iran could spiral into a military conflict on their doorstep with devastating economic effects, according to foreign diplomats, former U.S. officials and regional experts.

Even the most hawkish powers in the Persian Gulf, Saudi Arabia, the United Arab Emirates and Bahrain, which have backed Trump's tough line on Iran, were stunned by the attack on Soleimani and have appealed to the White House to avoid a conflagration with Tehran, the sources said.

While the Saudis and the Emiratis privately welcomed Soleimani's demise, they worry their close proximity to Iran makes them vulnerable if a war erupts and fear Trump's unpredictable decision-making could trigger a conflict no one wants, jeopardizing a yearslong effort to promote tourism and financial services.

"Everyone from Kuwait to Oman is fearful of escalation," said a former U.S. intelligence official recently returned from a visit to the region. "Everyone realizes that a military conflict could be a disaster."

If one stray missile hits an office tower in Dubai, "its reputation as a financial center is in jeopardy," the former official added.

Immediately after the Jan. 3 strike, Saudi Crown Prince Mohammed bin Salman dispatched his younger brother, Deputy Defense Minister Khalid bin Salman, to Washington to meet Trump and other top officials. He conveyed a message from Riyadh urging the U.S. to "de-escalate," two former U.S. officials and two foreign diplomats said.

The Saudi minister of state for foreign affairs, Adel al-Jubeir, tweeted hours after the strike that the kingdom stressed "the importance of de-escalation to save the countries of the region and their people from the risks of any escalation." And the Saudi minister of foreign affairs, Prince Faisal bin Farhan, said Jan. 6 that Riyadh remained "very keen" to defuse the tensions.

"I think the most important thing that they had on the agenda was to say, 'Look, you have to defend yourselves and everything, but we really, really, really don't want an escalation,'" said Hussein Ibish, a senior resident scholar at the Arab Gulf States Institute think tank.

As commander of the Revolutionary Guard's Quds Force, Soleimani oversaw a Shiite proxy network across the Middle East that Gulf Arab states viewed as a dangerous threat. But the Gulf countries recognize Iran retains the force that Soleimani helped build, and there is no sign Tehran is ready to pull back on its ambitions in the region, Ibish said.

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As a result, several Persian Gulf governments are searching for a diplomatic way out of the crisis. Since Soleimani was killed, Qatar's emir, Sheikh Tamim bin Hamad al-Thani and his foreign minister, Mohammed bin Abdulrahman Al Thani, have flown to Tehran for talks and spoken to their American counterparts.

Even before the drone strike on Soleimani in Baghdad, both Saudi Arabia and the UAE had reached out discreetly to Tehran to try to lower the temperature, foreign diplomats and former officials said.

Unlike the Saudis or the Emiratis, leaders in Kuwait, Oman and Qatar have long harbored reservations about the Trump administration's "maximum pressure" campaign against Shiite-ruled Iran, and have favored diplomacy over sanctions and military confrontation.

But the crisis with Iran has produced a rare moment of unity among the Gulf Arab states, with all Gulf Cooperation Council governments issuing similar public statements in recent days calling for restraint and dialogue and warning of the risks of further escalation.

Recounting his conversations with allies around the world after the strike on Soleimani, Secretary of State Mike Pompeo has praised partners in the Middle East for what he called their supportive stance, while complaining about the skepticism of European governments.

An 'irrational actor'

"The Brits, the French, the Germans all need to understand that what we did, what the Americans did, saved lives in Europe as well," he said. "This was a good thing for the entire world, and we are urging everyone in the world to get behind what the United States is trying to do to get the Islamic Republic of Iran to simply behave like a normal nation."

European governments have called for calm and long opposed Trump's decision to pull the U.S. out of the nuclear agreement between Iran and world powers. Privately, European diplomats expressed alarm at the killing of Soleimani, viewing it as a high-risk move that illustrated how the U.S. under Trump's leadership was an erratic player on the world stage that could not be relied on.

"The United States is now an irrational actor and that's something we have never seen before," one European diplomat, who was not authorized to speak on the record, told NBC News.

While the drone strike deepened the transatlantic divide over Iran, Gulf allies in Riyadh and Abu Dhabi still view Trump as a staunch ally who shares their view of Tehran and who will not raise uncomfortable questions over their human rights records.

"In their perception, President Trump is still their best bet," said Yasmine Farouk, a visiting fellow at the Carnegie Endowment for International Peace.

Saudi Arabia and the UAE in particular had grown frustrated with Trump's predecessor, with officials privately scoffing at former President Barack Obama's emphasis on human rights and what they saw as an overly conciliatory approach to Iran in nuclear negotiations.

But Trump's oft-stated desire to pull the U.S. out of "endless wars" in the Middle East, and his on-again-off-again approach to the American military presence in Syria, Iraq and elsewhere, have prompted the Gulf Arab states to question whether the U.S. would come to their aid at a moment of peril.

"They believe the United States is less reliable as a partner than it used to be," said Gerald Feierstein, a retired diplomat who held senior posts across the Middle East.

Even before Trump entered office, the Gulf Arab states had looked to reduce their reliance on Washington and searched for other economic and security partners abroad to hedge their bets, Feierstein said. They have forged closer ties with Russia and China and tried to flex their military muscle, including in Yemen where a Saudi-led intervention has floundered.

The Gulf governments are still trying to figure out if the strike against Soleimani was a one-off or part of a more concerted campaign, said Feierstein, now a senior vice president at the Middle East Institute think tank.

"If I were the Saudis or the Emiratis, I would like to know what exactly is Act II of this play."