US President Donald Trump said he called off retaliatory strikes on three Iranian sites following the downing of a US Navy drone because the action would not have been proportionate.

“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, Trump tweeted Friday. 10 minutes before the strike I stopped it.”

A commander in the Islamic Revolutionary Guard Corps told a semi-official news agency on Friday that the drone had been accompanied by a manned US spy plane that Iranian forces decided not to target.

The planned US attack, ordered after Iranian forces shot down a US Navy drone over the Strait of Hormuz, would have involved airstrikes and was close to being carried out when it was stopped, said another official, who would not discuss whether the plan might still be revived. The officials were granted anonymity to discuss a national security matter.

National Security Advisor John Bolton was pushing for the strike. Trump changed his mind based on some additional information on Iranian decision making, one of the officials said. Iran was not given any warning of possible retaliation.

With tensions still high, the Iranians called the Swiss ambassador, Markus Leitner, into the Foreign Ministry for talks. The Swiss embassy also represents US interests in Iran, and the Swiss envoy traditionally serves as the conduit for messages between the two nations, which have no diplomatic relations. But Brian Hook, the US special representative for Iran, told reporters the Iranians continue to reject diplomatic overtures to de-escalate tensions in the region.

Airstrikes would have raised the spectre of a far broader conflict in the volatile region, which supplies one-third of the world’s oil. The move and its reversal underscore the wavering approach the President has shown at times regarding military force. He has repeatedly and fiercely lashed out at Iran and North Korea, but then cooled his rhetoric when hostilities threatened to erupt into open conflict. On two occasions since he took office, he has ordered limited military strikes on Syria.

Brent oil pared its biggest weekly gain in four months on the shifting developments. Futures erased gains in London on Friday, but are still up 4 per cent for the week.

Iran’s Deputy Foreign Minister for Political Affairs, Seyed Abbas Araghchi, said the country had indisputable evidence the US drone had violated Iranian air space, and state TV showed what it said were recovered parts of the downed aircraft. The Islamic Republic of Iran would not hesitate for a moment to decisively defend its territory against any aggression, Araghchi said in a statement released by the Ministry of Foreign Affairs on Friday.

Before the strike was called off, there were discussions on Thursday about whether to heighten security and awareness at sensitive domestic sites, one of the officials said.

Earlier on Thursday, as the attack was being planned, Trump downplayed Iran’s strike on the US Navy drone in the Persian Gulf that escalated regional tensions and fuelled a surge in oil prices, suggesting a loose and stupid individual may have been responsible for the strike.

“I would imagine it was a general or somebody, who made a mistake by shooting that drone down,” Trump said during an Oval Office meeting on Thursday with Canadian Prime Minister Justin Trudeau. “I find it hard to believe it was intentional. It could have been somebody who was loose and stupid.”

The operation was first reported by the New York Times , which said that Trump had pulled back as warplanes were in the air. One of the US officials disputed that part of the Times account.

The White House declined to comment on the reports and an official at the State Department didn’t immediately respond to a request for comment.

The President is in an increasingly difficult position on Iran. His administration has blamed the Islamic Republic for a series of attacks in the Gulf region since mid-May, including one last week on two oil tankers, but with little consequence for Tehran. He’s shown a desire to project American power, yet during the 2016 election he promised to extricate the US from foreign conflicts, an issue that’s sure to come up as his re-election campaign begins.

The US has directed additional forces to West Asia in recent weeks, but the numbers -- about 2,000 troops in total -- have been modest and haven’t come with clear indications of where they would be sent or what their mission would be. In some cases, forces already planned for deployment to the region had their arrival accelerated, while troops scheduled to depart saw their tours extended.

A military assault by the US could have immediate and far-reaching consequences. With proxy forces or allies in countries including Lebanon, Syria, Iraq and Yemen, among others, retaliation from Iran could come in many forms, targeting not just US interests but Israel as well and raising the risk of disruptions to oil flows out of the wider Persian Gulf region.

With Iran threatening the freedom of navigation in the Strait of Hormuz, Hook told reporters at a Saudi air base in Kharj, “it’s important that we deny Iran a foothold in the Gulf. It’s very important that we restore deterrence in this region.”

The last time the US launched a significant military effort against Iran was Operation Praying Mantis in 1988. In that operation, US Navy ships sank two Iranian ships and destroyed two Iranian surveillance platforms.

The move came after the USS Samuel B. Roberts was damaged by a mine in the Persian Gulf. Later that year, a US Navy cruiser shot down an Iranian commercial aircraft on a scheduled flight in Iranian airspace, killing nearly 300 people. The US expressed regret for the loss of life and said it mistakenly targeted the plane. Iran said it was a deliberate and illegal act.

During his time in office, Trump has ratcheted up economic sanctions on Iran as part of his maximum pressure campaign against the Islamic Republic. Yet, he has also said he doesn’t want a war with Tehran and that he is hoping Iran will reach out to negotiate.

As tensions climbed on Thursday following the drone strike, regional analysts and lawmakers from both parties warned that the likelihood of a bigger confrontation could be looming, whether intentional or not.

“The President may not intend to go to war here, but we’re worried that he and the administration may bumble into a war,” Senate Minority Leader Chuck Schumer, a New York Democrat, told reporters on Thursday after a briefing at the White House.

The top Republicans in the Senate and House both called separately for Trump to take a measured response to the Iranian actions.

Saudi Vice Minister of Defense, Khalid bin Salman, said he met Hook, the US special representative to Iran, to explore the latest efforts to counter hostile Iranian acts and continuous escalation that threaten the region’s security and stability. In a series of posts on Twitter, the minister affirmed Saudi Arabia’s support for the US maximum pressure campaign on Iran.

The US said the Global Hawk drone was flying in international airspace about 34 km (20 miles) away from Iranian territory when it was shot down.

This was an unprovoked attack on a US surveillance asset in the international airspace, said Navy Captain Bill Urban, a spokesman for US Central Command.

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