Donald Trump has sought to explain why he abandoned plans to launch airstrikes on Iran, claiming US forces were "cocked and loaded to retaliate".

In a series of tweets on Friday morning, the US president claimed he called off the operation over a fear the likely loss of life would be "not proportionate" to the downing of a US drone in the Strait of Hormuz.

"On Monday they shot down an unmanned drone flying in International Waters," Mr Trump incorrectly said. The drone was shot down on Thursday.

"We were cocked & loaded to retaliate last night on 3 different sights (sic) 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. I am in no hurry, our Military is rebuilt, new, and ready to go, by far the best in the world.

Tensions high as Trump approves new Iran sanctions: In pictures Show all 17 1 /17 Tensions high as Trump approves new Iran sanctions: In pictures Tensions high as Trump approves new Iran sanctions: In pictures Iran claims that in this picture released by Iran state TV, their surface-to-air missile is seen as it shoots down a US surveillance drone EPA Tensions high as Trump approves new Iran sanctions: In pictures This photo shows US RQ-4A Global Hawk unmanned surveillance drone. A drone of this model was shot down by Iran on Thursday 21 June AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures An oil tanker is on fire after it was subject to a suspected attacked at the Gulf of Oman on June 13. The US has blamed Iran for the attack Reuters Tensions high as Trump approves new Iran sanctions: In pictures Iran claims that in this picture released by Iran state TV, debris from the downed US drone is seen after it was recovered from Iranian waters AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures Smoke billows from an oil tanker after it was subject to a suspected attacked at the Gulf of Oman on June 13 Reuters Tensions high as Trump approves new Iran sanctions: In pictures US President Trump holds up a signed executive order to increase sanctions on Iran on 24 June AP Tensions high as Trump approves new Iran sanctions: In pictures Iranian President Rouhani stated in a televised address that the White House is "afflicted by mental retardation" following the increase in sanctions on 25 June EPA Tensions high as Trump approves new Iran sanctions: In pictures An Iranian navy boat tackles the fire on the Norwegian owned Front Altair oil tanker after it was hit in a suspected attack AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures Iran claims that in this picture released by Iran state TV, debris from the downed US drone is seen after it was recovered from Iranian waters AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures Smoke billows from an oil tanker after it was subject to a suspected attacked at the Gulf of Oman on June 13 Reuters Tensions high as Trump approves new Iran sanctions: In pictures A screenshot from a video released by the US Department of Defense that the US claims to show Iranian removing an unexploded limpet mine form the hull of the Japan-owned ship that was attacked in the Gulf of Oman on June 13 Getty Tensions high as Trump approves new Iran sanctions: In pictures An item reportedly found on the Japan-owned oil tanker that was attacked on June 13 in the Gulf of Oman AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures A handout photograph from the US Department of Defense shows a composite material that the US claim was left behind on the hull of the Japan-owned oil tanker following the removal of an unexploded limpet mine Getty Tensions high as Trump approves new Iran sanctions: In pictures A view from the cabin of an Iranian navy boat as it tackles the fire on the Norwegian owned Front Altair oil tanker after it was hit in a suspected attack EPA Tensions high as Trump approves new Iran sanctions: In pictures Release by US government A picture released by U.S. Central Command shows damage to the hull of the oil tanker Kokuka Courageous. The picture suggests that the ship is 'likely' to have been hit by a mine as the US Secretary of State Mike Pompeo moves to blame Iran for the suspected attack Reuters Tensions high as Trump approves new Iran sanctions: In pictures Smoke billows from an oil tanker after it was subject to a suspected attacked at the Gulf of Oman on June 13 Reuters Tensions high as Trump approves new Iran sanctions: In pictures Release by US government A picture released by U.S. Central Command shows damage to the hull of the oil tanker Kokuka Courageous. The pictures suggests that the ship is 'likely' to have been hit by a mine as the US Secretary of State Mike Pompeo moves to blame Iran for the suspected attack EPA

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

Mr Trump's outburst came after The New York Times reported he initially approved strikes against Tehran on Thursday, before backing down as planes were in the air.

Iranian officials said Tehran had received a message from Mr Trump warning a US attack on Iran was imminent but saying he was against war and wanted talks on a range of issues.

“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," one official told Reuters.

Another said: "We made it clear that the leader is against any talks, but the message will be conveyed to him to make a decision."

Mr Trump prefaced his explanation on Twitter by repeating his claim the 2015 nuclear agreement with Iran – negotiated by the Obama administration – was a "terrible deal" and that the Islamic Republic was now "bust".

"President Obama made a desperate and terrible deal with Iran - Gave them 150 Billion Dollars plus I.8 Billion Dollars in CASH!," Mr Trump tweeted. "Iran was in big trouble and he bailed them out.

"Gave them a free path to Nuclear Weapons, and SOON. Instead of saying thank you, Iran yelled Death to America. I terminated deal, which was not even ratified by Congress, and imposed strong sanctions.

"They are a much weakened nation today than at the beginning of my Presidency, when they were causing major problems throughout the Middle East. Now they are Bust!"

Iran military releases footage of 'missile strike on US drone'

In fact, the 2015 deal prevented Iran from building nuclear weapons until at least 2030, and Mr Trump's suggestion Iran is no longer causing "major problems" appears to contradict claims by his government the country was responsible for attacking two commercial oil tankers in the Gulf of Oman.

The circumstances of the shooting down of the drone, a US navy RQ-4A Global Hawk, by Iran’s Revolutionary Guard, are disputed.

Iran said the drone, with a wingspan larger than a Boeing 737 and costing more than over $100m (£79m), had violated its territorial airspace.

The US said the "unprovoked attack” happened in international airspace, but failed to provide compelling evidence for the claim. Either way, it marked the first time Iran had struck the US military, which released a set of coordinates it claimed the drone was shot down at.

Iranian foreign minister Mohammad Javad Zarif said on Twitter that the aircraft had taken off from the United Arab Emirates “in stealth mode & violated Iranian airspace”.

A Revolutionary Guards statement said the drone’s identification transponder had been switched off “in violation of aviation rules and was moving in full secrecy” when it was downed, Reuters quoted the Iranian state broadcaster IRIB as saying.