DUBAI—America’s Gulf allies are steeling themselves for a heavy U.S. bombardment of Iran that they expect to trigger a vicious cycle of retaliation against their own economic and civilian infrastructure as early as this week.

Their concerns are heightened by a lack of progress in the various efforts to reach a negotiated end to the conflict while the U.S. and Iran are threatening especially ferocious fighting if the conflict resurges.

President Trump has been leaning toward a large postelection attack that could target Iranian infrastructure and nuclear sites, but hasn’t decided whether to go ahead, The Wall Street Journal has reported. Iranian officials said over the weekend their response to any attack would be unrestrained.

“The only reason why I’m not finished with Iran is I want to be nice. I want to try and save all those lives if I can,” Trump said Sunday at a rally in Iowa ahead of Tuesday’s midterm elections. “But at some point we’re going to have to give them the hammer.”Governments including Qatar and the United Arab Emirates were running security drills—including at airports—and attendees at a major energy conference in Abu Dhabi were cutting short their stays on advice from their governments.

Schools in the capital of Saudi Arabia, which is also under fire from the Iran-backed Houthi militants in Yemen, will remain online this week. Dutch and Belgian embassies in the region warned Thursday that security conditions could deteriorate quickly in the region.

Anwar Gargash, senior foreign-policy adviser to the U.A.E.’s president, said at a security conference over the weekend that the country hopes the diplomatic efforts will pan out, but is “braced for the worst.”Egyptian Foreign Minister Badr Abdelatty said at the same conference that a new round of escalation would be more destructive and that efforts in the coming days or weeks would be critical to heading it off.

The U.S. military has prepared options for attacks—restocking munitions in the region and beefing up defenses, including by moving troops out of vulnerable bases and sending another Patriot antimissile system to Israel.

Trump has ramped up threats before, most recently in late July, only to back down in hopes of a negotiated deal.

Tehran politely welcomed a letter sent in late October by Vice President JD Vance seeking to open talks with Iran’s top national security official, Mohsen Rezaei. But so far it hasn’t responded formally to Vance’s request to discuss Iran’s nuclear program and hasn’t agreed to a meeting, mediators between the two sides said.

Talks in the main diplomatic channel, mediated by Qatar, are stuck on whether the U.S. or Iran should be the first to make concessions to move talks along, the mediators said.

Gulf states are growing alarmed that they may face more destructive Iranian attacks than at the height of the war in March. Iran lacks the firepower to blunt U.S. and Israeli airstrikes and has adopted a strategy of quickly raising the stakes in any exchange by attacking its more vulnerable neighbors across the Persian Gulf.

Iran has threatened publicly and in private diplomatic communications to attack a broad array of U.S. and Gulf targets in the region in response to any U.S. strike.

“There is no world in which a short and sharp strike by the U.S. will be absorbed by Iran,” said Behnam Ben Taleblu, senior director of the Iran program at U.S. think tank Foundation for Defense of Democracies. “An intense infrastructure-based targeting campaign by Washington is likely to beget one by Tehran against U.S. partners.”Some Arab states have warned Iran they could retaliate individually or collectively if Tehran targets their infrastructure, the mediators said. The U.A.E. carried out strikes on Iran over the spring, but other Gulf states largely sat out the fighting. Gulf states are scrambling to come up with new formulas to break the diplomatic deadlock.

Qatari mediators, who had previously proposed a seven-day period in which the U.S. and Iran would lift their restrictions on traffic in Hormuz to build confidence for further talks, traveled to Tehran on Friday with a revised plan that would cut the confidence-building period to two days, Iran says. Under one of the proposals floated by Qatar, the U.S. would loosen its naval blockade if Iran halted attacks on shipping in the strait for an agreed number of days, the mediators and an Iranian official said.

Iran would then allow international nuclear inspectors back into the country and start a discussion on its stockpile of enriched uranium within a few days, they said. Once inspections are completed, the U.S. would lift some sanctions, they said. But Qatar has had difficulty nailing down an agreement.

The U.S. is reluctant to lift its blockade before clear progress on nuclear issues, fearing Iran will buy time by rushing bottled-up oil shipments out of the Gulf, mediators said. Iran’s Foreign Ministry spokesman said Monday there had been no discussion of nuclear issues. Iranian Deputy Foreign Minister Kazem Gharibabadi returned to Tehran from Doha on Sunday after talks failed to yield enough progress to trigger a visit from U.S. negotiators, mediators said.

Still, Iranian President Masoud Pezeshkian said Tehran was willing to continue talks.

“We are trying to solve the problem through dialogue. In this regard, the supreme leader of the revolution has also given the government certain powers,” he said without elaborating, state-run IRNA news agency reported Monday. Last week got off to an unpromising start when officials from Saudi Arabia and allied nations Pakistan and Turkey traveled to Tehran and expressed willingness to discuss a regional security agreement with Iran if it agreed to join talks on its nuclear program, people briefed on the discussions said.

At the meeting, Saudi Arabia also asked for Tehran’s help reining in attacks on the kingdom by the Iran-backed Houthi militants in Yemen.

Hours after the talks, the Houthis launched drone and missile attacks at targets including the capital, Riyadh, and the Persian Gulf oil hub Ras Tanura. Attacks have also continued at an unusually aggressive pace in the Strait of Hormuz as Iran tries to reassert control over the waterway.

“The U.S. and Iran clearly are on very different planes with regards to both their strategic end goals and the political priorities of their leaderships, which is to be at least seen as the victor of this conflict,” said Umer Karim, a researcher on Gulf security at the U.K.’s University of Birmingham.

“This creates an incredibly challenging situation for mediators and regional stakeholders who will all bear the brunt of this conflict.”The top U.S. commander in the Middle East briefed Trump on Thursday on military options for Iran, in a rare in-person visit to the White House as the U.S. weighs resuming major combat operations, The Journal reported. Adm.

Brad Cooper rarely briefs Trump in person, so the meeting could signal that the U.S. is moving closer to significant military operations.

“There are still substantive differences between both sides, so an escalation seems inevitable,” said Ali Vaez, an Iran expert and deputy Middle East program director at the International Crisis Group, a conflict-resolution organization. “Things will get nasty very quickly.”