Donald Trump said "Iran made a big mistake" in downing the drone. (Pictures: PA).
US President Donald Trump says he stopped plans to launch strikes against Iran after discovering how many people would be killed.
President Trump said the United States was "cocked and loaded" to strike Iran in retaliation for an American military drone being shot down.
He also confirmed he has "terminated" a nuclear deal with Iran and "imposed strong sanctions".
Posting on Twitter, he said the US military was "cocked and loaded to retaliate last night on three different sights" before he asked how many people would die as a result of strikes.
Upon being told 150 people would be killed, President Trump says he ordered strikes to be stopped, ten minutes before it was due to be launched.
President Trump continued by saying strikes were " not proportionate to shooting down an unmanned drone."
....On Monday they shot down an unmanned drone flying in International Waters. 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....— Donald J. Trump (@realDonaldTrump) June 21, 2019
....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
Since the drone was shot down, the US has barred American-registered aircraft from flying over Iranian-administered airspace in the Persian Gulf and the Gulf of Oman.
Iran claims the US drone entered their airspace on Thursday morning but the US maintains it was shot down in international airspace, with President Trump stating: "We have it all documented."
The US President also warned Iran had made "a very big mistake", and said "you'll find out" when asked how the US would respond.
It is the latest update in rising tensions between the two countries after Mr Trump accused Iran of sabotaging two oil tankers, and then subsequently announced the deployment of an additional 1,000 troops to the region earlier this week.
Iran denies involvement in the oil tankers incident.