'We were cocked and loaded': Trump confirms Iran strike plan

New York: US President Donald Trump has revealed he was prepared to launch a military strike against Iran but called it off with just ten minutes to spare when a military general told him it would cause 150 deaths.

Trump said on Twitter that casualties of that magnitude would not be a "proportionate" response to Iran's decision to shoot down an unmanned American drone flying over the Strait of Hormuz on Wednesday night local time.

Senior administration officials told reporters on Thursday night that Trump had approved military strikes against Iran before abruptly changing his mind.

US President Donald Trump confirmed reports he pulled out of a plan to launch a military strike on Iran in response to the shooting down of an American drone. Credit: AP

In a series of tweets on Friday morning Trump said: "We were cocked & loaded to retaliate last night on 3 different sights when I asked, how many will die.

"150 people, sir, was the answer from a General. 10 minutes before the strike I stopped it, not...proportionate to shooting down an unmanned drone."

Tensions between the US and Iran have escalated dramatically following the shooting down of the drone and attacks on two commercial tankers in the Gulf of Oman last week which the Trump administration has attributed to Iran.

The Trump administration insists the drone, worth US$130 million ($188 million), was shot down while flying in international waters. The Iranian government says it had entered the country's air space.

The US Federal Aviation Administration responded to the hostilities on Friday by banning US carriers from flying in Iran-controlled airspace over the Strait of Hormuz and Gulf of Oman.

Qantas is among the major airlines that has re-routed its flight routes to avoid entering potentially dangerous airspace over Iran.

Unlike more hawkish members of his administration, Trump has repeatedly indicated that he does not want the US to be drawn into another war in the Middle East.

"I am in no hurry, our Military is rebuilt, new, and ready to go, by far the best in the world," he said on Twitter on Friday.

"Sanctions are biting & more added last night. Iran can NEVER have Nuclear Weapons, not against the USA, and not against the WORLD!"

Trump, who withdrew from the Obama administration's nuclear deal with Iran last year, said Iran was a "much weakened nation today" since he came to office.

The President's decision not to retalliate angered some Republicans in Congress, including Wyoming congresswoman Liz Cheney.

A series of attacks on oil tankers near the Persian Gulf has ratcheted up tensions between the US and Iran.Credit: ISNA

“The failure to respond to this kind of direct provocation that we’ve seen now from the Iranians, in particular over the last several weeks, could in fact be a very serious mistake,” Cheney said on Friday.

But Republican congressman Matt Gaetz said: "I am grateful that the president is not eager to lurch into another Middle Eastern regime change, in an endless, unfocused, unconstitutional way.

"President Trump ran as a very different kind of Republican, someone who wanted to end wars not start them."

Senior Democrats, meanwhile, urged Trump to show restraint.

"There is no justification for further escalating this crisis - we need to step back from the brink of war," Democratic senator and 2020 presidential candidate Elizabeth Warren said.

Vermont senator Bernie Sanders called on Congress to "assert its constitutional authority and stop Trump from going to war".