Publicly, Iranian officials poured withering scorn on the prospect of any negotiations with the administration of US President Donald Trump.
But an apparent delay in a formal response to Pakistan, which delivered a 15-point proposal on behalf of the US, appeared to signal that at least some figures in Iran may be considering it.
Iranian Foreign Minister Abbas Araqchi suggested some willingness to negotiate an end to the war if Tehran's demands were met.
The exchange of messages through mediators "does not mean negotiations with the US," Araqchi said on state television.
"They put forward ideas in their messages that were conveyed to top authorities, and if necessary, a position will be announced by them," he said.
Additionally, Iran has told intermediaries that Lebanon must be included in any ceasefire agreement with the US and Israel, six regional sources familiar with Iran's position said.
Trump, speaking at an event in Washington, said Iranian leaders "are negotiating, by the way, and they want to make a deal so badly, but they're afraid to say it because they will be killed by their own people. They're also afraid they'll be killed by us."
Trump's 15-point proposal, sent through Pakistan, calls for removing Iran's stocks of highly enriched uranium, halting enrichment, curbing its ballistic missile program and cutting off funding for regional allies, according to three Israeli cabinet sources familiar with the plan.
Oil prices fell and shares regained some ground on Wednesday after reports that the US had sent the 15-point plan to Iran, with investors hoping for an end to a war that has killed thousands of people and disrupted global energy supplies.
The White House declined to disclose specifics of its proposal and threatened to escalate its strikes.
Three Israeli cabinet sources said Prime Minister Benjamin Netanyahu's security cabinet had been briefed on the US proposal.
They said its terms included removing Iran's stocks of highly enriched uranium, halting enrichment, curbing its ballistic missile program and ending funding for regional allies.
The Pentagon is meanwhile planning to send thousands of airborne troops to the Gulf to give Trump more options to order a ground assault, sources have told Reuters, adding to two contingents of Marines already on their way.
The first Marine Expeditionary Unit aboard a huge amphibious assault ship could arrive around the end of the month.
Pakistan has offered to host talks attended by senior US officials as soon as this week.
A senior ruling party official in Turkey, Harun Armagan, told Reuters the country was also "playing a role passing messages" between Iran and the US.
A senior Israeli defence official said Israel was sceptical Iran would agree to the terms, and that Israel was concerned that US negotiators might make concessions in any talks.
The war has raged on with no let-up in air attacks against Iran, or in Iranian drone and missile strikes against Israel and US allies.
An Israeli military official, asked whether Israel had adjusted its military plans since Trump said talks were under way, said it was "pretty much business as usual".
The Israeli military described several new waves of attacks on Iran during the day, including one on Iran's construction of ships and submarines.
Iranian SNN News Agency said a residential area was hit in Tehran, with rescuers searching the rubble.
Kuwait and Saudi Arabia said they had repelled new drone attacks.
Iran's Revolutionary Guards said they had launched new attacks against Israel and US bases in Kuwait, Jordan and Bahrain.
