Iran says it received a message from US President Donald Trump through Oman warning that an American attack was imminent.
Tehran claims Trump indicated he was opposed to war and wanted to hold talks with Iran amid escalating tensions and fears of a military confrontation in the Gulf of Oman.
Mr Trump reportedly approved military strikes against Iran in retaliation for the downing of a US surveillance drone, while planes were in the air.
The high-altitude drone was shot down by the Revolutionary Guard late Wednesday night with Iran claiming the unmanned aircraft was in its airspace and the US insisting it was taken out by a surface-to-air missile in international airspace over the Strait of Hormuz.
An Iranian official told Reuters that Tehran had Oman forwarded a message from Mr trump that a US attack was imminent.
The official said: "In his message, Trump said he was against any war with Iran and wanted to talk to Tehran about various issues ... he gave a short period of time to get our response but Iran's immediate response was that it is up to Supreme Leader (Ayatollah Ali) Khamenei to decide about this issue."
The second official said: "We made it clear that the leader is against any talks, but the message will be conveyed to him to make a decision.
"However, we told the Omani official that any attack against Iran will have regional and international consequences."
Russia, one of Iran's key allies, has accused the US of deliberately stoking dangerous tensions around Iran and pushing the situation to the brink of war, the RIA news agency reported.
Deputy Foreign Minister Sergei Ryabkov called on Washington to weigh the possible consequences of conflict with Iran and said a report in the New York Times showed the situation was extremely dangerous.
Mr Trump approved military strikes against Iran in retaliation for the downing of a US surveillance drone, but called off the attacks at the last minute, the report said.
An unnamed US official told the newspaper that warplanes took off and warships were put in position for a retaliatory attack, but the crews were told to stand down and no weapons were fired.
The dispute has had consequences for airlines and travellers, with some flights re-routing to avoid Iran-controlled airspace over the Strait of Hormuz and Gulf of Oman.
America's aviation regulator has barred its carriers from the area until further notice.
Tensions have escalated in recent weeks after attacks on six tankers along a crucial oil shipping route.
The US and Saudi Arabia, its major ally in the Middle East, have accused Iran of attacking the tankers.
Tehran has denied responsibility.
On Thursday, Trump said Iran had made "a very big mistake" by shooting down the drone in what the US military claimed was an "unprovoked attack".
Iran claimed the drone was flying in its airspace near the southern coast, and an official said the country would "strongly respond" to any violation of its "red line".
Brigadier General Hossein Salami, commander in chief of the Revolutionary Guards, said Iran does not want to enter a military conflict but "we are completely ready for the war".
Tensions between Iran and the US have escalated since last year when Mr Trump withdrew from a 2015 nuclear deal between Tehran and major powers and reimposed sanctions.
