President Donald Trump has not made a final decision on whether to carry out new strikes against Iran, according to two diplomats briefed on the matter who spoke on condition of anonymity.
The president, however, has repeatedly said he is weighing ordering new military action once the US's November 3 elections are over.
Those threats and the fresh US urgings for allies to prepare for potential retaliation are putting the region on alert that a return to major operations could now be on the horizon.
The White House and US officials declined to comment.
Iranian Foreign Minister Abbas Araghchi said in a post on X that Tehran "continues to give diplomacy a chance to succeed" and was working with mediators to review ideas that Tehran included in a proposal floated in September - summarily rejected by Trump - that the Iranians still wanted to see used as the basis to return to a ceasefire.
Meanwhile, the United Arab Emirates foreign ministry urged the sides to "exercise wisdom and pursue political solutions to help contain tensions" and prevent a return to full-scale operations in the war that began in late February.
The US had told regional allies that the new round of military action could last for several days, but regional officials were bracing for Iran and its proxy groups to retaliate, which could make the conflict last longer, the diplomats said.
The allies have also been urged by US officials to take precautionary measures in anticipation that Iran's response will include retaliatory strikes on energy facilities and other crucial infrastructure.
While the US has not carried out a strike against Iran since early September, the situation in the Middle East has become more complicated.
The conflict has spread, with Iran-backed Houthi rebels carrying out attacks on Saudi Arabia's oil infrastructure and airports.
A Saudi-led coalition has responded with its own deadly attacks on Houthi-held territory in Yemen.
Late on Wednesday, reports emerged that Defense Secretary Pete Hegseth had fired the Pentagon's top military planner.
Army Lieutenant General Brett Sylvia was removed as head of strategy, plans and policy on the Joint Chiefs of Staff.
A defence official who spoke on condition of anonymity said there was no immediate replacement for Sylvia and no reason had been given for the firing.
Trump, who has focused in recent weeks on campaigning for Republicans before the November 3 elections, has been evasive about what he plans to do next with Iran.
The war has proved to be a heavy weight on Republican candidates as they make their case to voters who are fatigued by rising petrol prices, a by-product of the war that has driven up costs across nearly every sector in the global economy.
While campaigning for Republicans, Trump has consistently assured voters that the war's end is near, while also threatening that a new round of bombing could be coming once the election passes.
During a campaign stop in Lubbock, Texas, on Tuesday, Trump said a conclusive end to the conflict could be coming "in a couple of weeks, if you don't mind".
"Somebody asked me before, when will the war in Iran end?" Trump said earlier in the same address.
"I said, 'Whenever I want it to end.' It'll be very quick, but we have to have it end properly, with total and complete - a total statement, they will never have a nuclear weapon."
