US President Donald Trump has said he stopped air strikes on targets in Iran because he was told 150 people would die as a result.
He said he scrapped the attacks ten minutes before the strikes after a general told him of the potential death toll that could result.
It came after Iran shot down a US drone in what the president termed a "big mistake".
Iran said earlier it had recovered parts of a US Global Hawk spy drone in its territorial waters after downing the aircraft in a missile strike, but the Pentagon says it was above international waters when it was hit.
....proportionate to shooting down an unmanned drone. I am in no hurry, our Military is rebuilt, new, and ready to go, by far the best in the world. Sanctions are biting & more added last night. Iran can NEVER have Nuclear Weapons, not against the USA, and not against the WORLD!
— Donald J. Trump (@realDonaldTrump) June 21, 2019
Iranian officials told Reuters that it had received a message from Mr Trump through Oman overnight warning that a US attack on Iran was imminent.
"In his message, Trump said he was against any war with Iran and wanted to talk to Tehran about various issues," one of the officials told Reuters.
"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."
A second Iranian 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."
This morning, Iran said that it had "indisputable" evidence that the drone had violated its airspace.
Deputy foreign minister Abbas Araghchi told Swiss ambassador, Markus Leitner, whose country represents US interests in Iran, of the evidence last night, the foreign ministry said in a statement.
"Even some parts of the drone's wreckage have been retrieved from Iran"s territorial waters," Mr Araghchi told the Swiss envoy.
Meanwhile, the US has banned American civilian flights from the area as tensions between the two countries increases further after a series of attacks on tanker ships the US blamed on Tehran.
The US Federal Aviation Administration warned of danger to flights "demonstrated by the Iranian surface-to-air missile shoot-down of a US unmanned aircraft system".
It barred American civilian aircraft from the area where it took place "until further notice".
The Pentagon denounced the "unprovoked attack", claiming the navy drone was 34km from Iran when destroyed by a surface-to-air missile.
But the Islamic Revolutionary Guard Corps said it brought the drone down as it was "violating Iranian air space" over the waters of Hormozgan province.
Iranian Foreign Minister Mohammad Javad Zarif provided coordinates to back the claim.
"At 00:14 US drone took off from UAE in stealth mode & violated Iranian airspace," he tweeted. "It was targeted at 04:05 at the coordinates (25°59'43"N 57°02'25"E) near Kouh-e Mobarak."
"We've retrieved sections of the US military drone in OUR territorial waters where it was shot down."
At 00:14 US drone took off from UAE in stealth mode & violated Iranian airspace. It was targeted at 04:05 at the coordinates (25°59'43"N 57°02'25"E) near Kouh-e Mobarak.
— Javad Zarif (@JZarif) June 20, 2019
We've retrieved sections of the US military drone in OUR territorial waters where it was shot down. pic.twitter.com/pJ34Tysmsg
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