President Donald Trump says he does not believe the shooting down of a US military drone by Iran was "intentional", in an apparent turnaround amid fears the escalating tensions between the two countries could spark an open confrontation in the Gulf.

Hours after tweeting on Thursday that "Iran had made a very big mistake" in downing the unmanned aircraft, Trump told reporters that it could have an error by a "loose and stupid" Iranian general.

Earlier in the day, the two countries offered differing accounts over the incident.

Washington said the drone had been downed in international airspace over the Strait of Hormuz by an Iranian surface-to-air missile. But Tehran disputed where the incident took place, saying the drone had violated Iranian airspace over the southern coastal province of Hormozgan.

Iranian Foreign Minister Mohammad Javad Zarif, in a Twitter post, gave the exact coordinates at which he said the drone was shot, adding that Iran has retrieved sections of the drone from its territorial waters.

The US Pentagon later released an image it said showed the flight path for the downed drone, but did not immediately provide a detailed explanation of the image.

Zarif pledged to prove the Iranian case at the United Nations, condemning Washington's "new aggression".

The incident marked the first direct Iranian-claimed attack on US assets and came amid heightened tensions between the US and Iran, triggered by Trump's decision last year to withdraw from an international accord that curbed Tehran's nuclear programme.

The downing of the drone was also the latest in an escalating series of incidents in the Gulf since mid-May, including suspected attacks on six tankers that the US blamed on Iran.

Tehran denied involvement, but Washington has since boosted its military presence in the Gulf, citing unspecified threats from Iran. All of this has raised fears that a miscalculation or a further rise in frictions could push the US and Iran into an open conflict.


Iran's Revolutionary Guard shoots down US drone (3:21)
"Iran made a very big mistake," Trump told reporters at the White House.

"This country will not stand for it, that I can tell you."

Asked if the US would respond, Trump replied: "You'll soon find out". But he also appeared to downplay the incident, saying it could have been an accidental move by someone who was "loose and stupid".

"I find it hard to believe it was intentional," Trump said, adding: "I think probably Iran made a mistake - I would imagine it was a general or somebody that made a mistake in shooting that drone down."

'Unprovoked attack'
Iran's paramilitary Revolutionary Guard Corps (IRGC) said it downed the drone at 4:05am local time when the aircraft entered Iranian airspace near the Kouhmobarak district in southern Hormozgan. Iran used its air defence system known as Third of Khordad to shoot down the drone - a truck-based missile system that can fire up to 30km high, the semi-official Fars news agency reported.

Iran's state-run IRNA news agency, citing the IRGC, identified the drone as an RQ-4 Global Hawk, which can cost close to to $150m apiece, can fly higher than 16km and stay in the air for more than 24 hours at a time.

Zarif, in his Twitter post, said the drone had taken off from the United Arab Emirates in "stealth mode" to avoid detection.

"We'll take this new aggression to UN & show that the US is lying about international waters," he tweeted. "We don't seek war, but will zealously defend our skies, land & waters."

At 00:14 US drone took off from UAE in stealth mode & violated Iranian airspace. It was targeted at 04:05 at the coordinates (25°59'43"N 57°02'25"E) near Kouh-e Mobarak.

We've retrieved sections of the US military drone in OUR territorial waters where it was shot down.But the US Central Command (CENTCOM) called the Iranian reports "false", saying the incident "was an unprovoked attack on a US surveillance asset in international airspace".

The unmanned aircraft was 34km from the nearest Iranian territory when it was hit, said Joseph Guastella, commander of CENTCOM. He offered a different take than Trump on the incident, called it "an attempt to disrupt our ability to monitor the area following recent threats to international shipping and free flow of commerce".

Independent confirmation of the drone's location when it was brought down was not immediately available.

Justin Bronk, research fellow at the Royal United Services Institute, described the US drone as "very sophisticated" and said it was unlikely that the unmanned aircraft would have strayed accidentally into Iranian airspace.

"It's got extremely powerful terrain and maritime surveillance mapping radar, as well as electro-optical and infrared sensors. So it has a very sophisticated set of sensors to tell it exactly where it is at any given time," he said.

"This is one of the least likely drones in the world to get lost ... So that leaves you with either the Iranians shooting it down in international airspace, as a controlled escalation or warning to the US and international community that the status quo with the sanctions, particularly on oil exports is intolerable. Or you could argue, potentially that the drone strayed into Iranian airspace deliberately," he said.

The latter explanation was less likely, he said, because the drone "is a very expensive and relatively scarce asset," meaning "the US would be more than symbolically annoyed at losing it."

'Borders are our red line'
In Iran, General Hossein Salami, the IRGC commander, said Iran did not seek conflict with any country, but added: "We are fully ready for war". Speaking to a crowd in the western city of Sanandaj, Salami described the US's drone as "violating our national security border".

"Borders are our red line," Salami said. "Any enemy that violates the borders will be annihilated."

In Washington, Senator Lindsey Graham, a key Republican ally of Trump, said the president's "options are running out" and that the US and Iran were "one step closer" to conflict.

But Trump's opponent, the Democratic speaker of the House of Representatives, Nancy Pelosi, warned that "there's no appetite for wanting to go to war in our country".

Senator Chuck Shumer, also a Democrat, accused the president of "driving us toward another endless conflict in the Middle East".

Meanwhile, Russian President Vladimir Putin called for caution, warning any war between Iran and the US would be a "catastrophe for the region as a minimum".

Saudi Arabia, Washington's main Gulf ally, said Iran had created a grave situation with its "aggressive behaviour" and the kingdom was consulting other Gulf Arab states on next steps.

"When you interfere with international shipping it has an impact on the supply of energy, it has an impact on the price of oil which has an impact on the world economy. It essentially affects almost every person on the globe," Adel al-Jubeir, Saudi minister of state for foreign affairs, told reporters in London.

Antonio Guterres, the UN secretary-general, said he was concerned by the latest incident, and called on all parties to "exercise maximum restraint and avoid any action that could inflame the situation".