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 delivering 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.
The senior Iranian official's comments to Reuters that the proposal was still under review - though the initial response was "not positive" - appeared to contradict a report by Iran's Press TV that cited an unidentified official as saying Iran had rejected it.
A senior Pakistani security official said that Pakistan had followed up with Iran's foreign minister and was still awaiting a formal reply.
A second Pakistani source said: "The Iranians told us they will get back to us tonight. The media is reporting they've said no. But we have not received any official confirmation from Iran. So we are just waiting. They are all underground and communication is big challenge."
Another senior Iranian official had earlier confirmed that Iran had received a proposal and said that talks, if they went ahead, could be held in either Pakistan or Turkey.
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 senior Pakistani security official said Pakistani intelligence had delivered the US proposal to Iran, and Foreign Minister Ishaq Dar had followed up with Iranian Foreign Minister Abbas Araqchi.
So far there had been no response from the Iranian side or any confirmed dates or venue for talks, the Pakistani official said.
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 that 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.
