Trump claims 'disproportionate' Iran strikes scrapped to save 150 lives

US President Donald Trump claimed he called off planned strikes on Iran because the expected death toll of 150 people would not have been a "proportionate" response to Tehran shooting down an American drone.

The downing of the drone - which Iran insists violated its airspace, a claim Washington denies - has seen tensions between the two countries spike further after a series of attacks on tankers the US has blamed on Tehran.

Under pressure to respond to the high-stakes incident near the strategic Strait of Hormuz, Trump said the US was "cocked & loaded to retaliate" on Thursday night by hitting "3 different sites," but that he scrapped the strikes just 10 minutes before they were carried out.

"I asked, how many will die. 150 people, sir, was the answer from a General," the president tweeted, saying he concluded it would not have been "proportionate to shooting down an unmanned drone."

"I am in no hurry, our Military is rebuilt, new, and ready to go," he wrote.

The US president had struck a combative tone in his initial public comments about Iran shooting down the Global Hawk surveillance aircraft.

"Iran made a very big mistake!" he tweeted, later adding at the White House: "This country will not stand for it, that I can tell you."

But as the pre-dawn incident whipped up fears of open conflict between the United States and its declared foe Iran, Trump moved to dial back tensions.

"I find it hard to believe it was intentional, if you want to know the truth," Trump said.

On Friday, Iran vowed to defend its borders after downing the drone, with the commander of the aerospace arm of its elite Revolutionary Guards saying the aircraft was warned twice before it was fired on over the Gulf of Oman.

Iran said it had called in the Swiss ambassador, whose country has represented US interests since the severance of diplomatic relations in the aftermath of the Islamic revolution of 1979, to issue a formal protest. 

But the US special representative on Iran, Brian Hook, said Tehran was "responsible for escalating tensions in the region" and accused it of rejecting diplomatic overtures to deescalate the situation.

"Iran needs to meet diplomacy with diplomacy, not military force," Hook told reporters in Saudi Arabia.

Iran's deputy foreign minister Abbas Araghchi provided the ambassador with "indisputable" evidence the drone had violated Iranian airspace, the foreign ministry said.

Araghchi "reiterated that Iran does not seek a war and conflict in the Persian Gulf," but warned: "The Islamic Republic of Iran would not hesitate for a moment to decisively defend its territory against any aggression."

Iranian television later broadcast images of what it said was "debris" of the downed drone recovered from Iran's territorial waters.

"The debris was floating. We recovered it from the sea inside our territorial waters," a general said.

Meanwhile, the UN chief recommended “nerves of steel” be deployed in the face of soaring tensions between the US and Iran.

Secretary-General Antonio Guterres said “I have only one strong recommendation: nerves of steel”, according to UN spokeswoman in Geneva Alessandra Vellucci.

The comments came after Iran said it was notified of an imminent overnight US attack via Oman, officials told Reuters on Friday.

The officials said US President Donald Trump’s message was relayed to Tehran by authorities in Oman, deemed to be the regional mediator for various issues.

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