Qatari mediators said the United States was reluctant to lift its naval blockade before clear progress on nuclear issues because it feared Iran would buy time by rushing bottled-up oil shipments out of the Gulf. Under one proposal floated by Qatar, the United States would loosen the blockade if Iran halted attacks on shipping in the Strait of Hormuz for an agreed number of days, the mediators and an Iranian official said. Iran would then allow international nuclear inspectors back and begin discussing its enriched-uranium stockpile within a few days, and the United States would lift some sanctions once inspections were completed, they said.

Qatar had difficulty nailing down an agreement. Gulf states were scrambling for new formulas to break the diplomatic deadlock. Qatari mediators had previously proposed a seven-day period in which the United States and Iran would lift their restrictions on traffic in the Strait of Hormuz to build confidence for further talks. The mediators traveled to Tehran on Friday with a revised plan that would cut the confidence-building period to two days, Iran said.

Iran’s Foreign Ministry spokesman said Monday that 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.

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.

Tehran politely welcomed a late-October letter sent by Vice President JD Vance seeking to open talks with Iran’s top national security official, Mohsen Rezaei. Iran had not formally responded to Vance’s request to discuss its nuclear program or agreed to a meeting, mediators said. The main diplomatic channel, mediated by Qatar, remained stuck over whether the United States or Iran should make the first concessions.

Gulf allies were preparing for the possibility of a heavy U.S. bombardment of Iran and expected any attack to trigger a vicious cycle of retaliation against their economic and civilian infrastructure as early as this week. Their concern had heightened because efforts to reach a negotiated end to the conflict had made little progress while the United States and Iran threatened especially ferocious fighting if the conflict resumed.

President Trump had been leaning toward a large postelection attack that could target Iranian infrastructure and nuclear sites, but he had not decided whether to proceed, The Wall Street Journal reported. At a rally in Iowa on Sunday, ahead of Tuesday’s midterm elections, Trump said, “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,” before adding, “But at some point we’re going to have to give them the hammer.” Iranian officials said over the weekend that Iran’s response to any attack would be unrestrained. Trump had escalated similar threats most recently in late July, only to back down in hopes of a negotiated deal.

The U.S. military had prepared options for attacks on Iran by restocking munitions in the region, strengthening defenses, moving troops out of vulnerable bases and sending another Patriot antimissile system to Israel. Adm. Brad Cooper, the top U.S. commander in the Middle East, briefed Trump on Thursday about military options for Iran during a rare in-person visit to the White House as the United States weighed resuming major combat operations. The Wall Street Journal said Cooper rarely briefed Trump in person and that the meeting could signal the United States was moving closer to significant military operations.

Governments including Qatar and the United Arab Emirates were running security drills, including exercises at airports. Attendees at a major energy conference in Abu Dhabi were cutting short their stays on advice from their governments. Schools in Riyadh, the Saudi capital, would remain online this week while the city was also under fire from the Iran-backed Houthi militants in Yemen. Dutch and Belgian embassies in the region warned Thursday that security conditions could deteriorate quickly.

Anwar Gargash, senior foreign-policy adviser to the United Arab Emirates’ president, said at a security conference over the weekend that the country hoped the diplomatic efforts would pan out but was “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.

Gulf states were growing alarmed that they could face more destructive Iranian attacks than at the height of the war in March. The Wall Street Journal reported that Iran lacked the firepower to blunt U.S. and Israeli airstrikes and had adopted a strategy of quickly raising the stakes in any exchange by attacking more vulnerable neighbors across the Persian Gulf. Iran had 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.

Behnam Ben Taleblu, senior director of the Iran program at the U.S. think tank Foundation for Defense of Democracies, said, “There is no world in which a short and sharp strike by the U.S. will be absorbed by Iran.” He added, “An intense infrastructure-based targeting campaign by Washington is likely to beget one by Tehran against U.S. partners.” Some Arab states warned Iran that they could retaliate individually or collectively if Tehran targeted their infrastructure, mediators said. The United Arab Emirates had carried out strikes on Iran over the spring, while other Gulf states had largely sat out the fighting.

Last week, officials from Saudi Arabia and the 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. Saudi Arabia also asked Tehran for 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 Riyadh and the Persian Gulf oil hub Ras Tanura.

Attacks had continued at an unusually aggressive pace in the Strait of Hormuz as Iran tried 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.” Ali Vaez, an Iran expert and deputy Middle East program director at the International Crisis Group, a conflict-resolution organization, said, “There are still substantive differences between both sides, so an escalation seems inevitable.” He added, “Things will get nasty very quickly.”