President Donald Trump said on Friday on Twitter that a strike against Iran in response to the attack on a US drone was ready to go Thursday evening, but he called it off at the last moment.

He tweeted that a general told him 150 Iranian people would die in the retaliation.

The president added that he thought such a move would be an escalation of force, one disproportionate to Iran's actions.

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President Donald Trump tweeted Friday morning that he was "cocked and loaded" to retaliate against Iran after its forces shot down a US drone earlier this week but decided not to at the last minute.

The president said he was concerned that the planned retaliatory strikes would be an escalation of force. "I asked, how many people will die," Trump said, adding that an unnamed military officer, a "general," told him that 150 Iranian people would die.

He said such a strike was "not proportionate to shooting down an unmanned drone." Trump added that he called everything off 10 minutes before the attack. The president also suggested he was "in no hurry" to go to war.

The retaliatory action the administration had planned was in response to an attack on a US Navy Broad Area Maritime Surveillance (BAMS-D) aircraft, specifically a RQ-4A Global Hawk high-altitude long-endurance (HALE) drone operating in international airspace.

Read more: Iran just shot down one of the US military's most advanced drones — it costs more than an F-35 stealth fighter

The incident marked a major escalation in tension between Tehran, Iran's capital, and Washington in the wake of a string of attacks on commercial tankers and a near miss when the crew of an Iranian gunboat took a shot at a US MQ-9 Reaper drone but failed to take it down.