Donald Trump says the Iranian military 'made a very big mistake' when it shot down an American spy drone.

Trump wasn't ready to say Thursday how he plans to respond. He indicated to reporters in the Oval Office that he believes it was an accident and not ordered by the Iranian government.

'Obviously you know, we're not going to be talking to much about it,' he said of the possibility of war. 'You'll find out.'

The president said it was someone 'loose and stupid' who did it and he has a 'big, big feeling' that someone made a mistake.

'I have a feeling that it was a mistake made by somebody who shouldn't have been doing it,' he assessed, possibly a rogue general.

Trump suggested that loss of life would change his calculus. 'We didn't have a man or woman in the drone,' he argued. 'It would have made a big, big difference.'

But he promised the U.S. would not leave the attack unanswered. 'This country will not stand for it, that I can tell you,' he said.

International leaders did not rush to judgment. Russian President Vladimir Putin simply said of a confrontation, 'It would be a catastrophe for the region as a minimum.'

Donald Trump says the Iranian military 'made a very big mistake' when it shot down a spy drone

Trump wasn't ready to say Thursday how he plans to respond. He indicated to reporters in the Oval Office that he believes the it was an accident

Pentagon map shows where it says the drone was shot down over international waters

The U.S. is calling the strike on a $180 million spy drone an 'unprovoked attack.' Trump says it took place over international airspace.

Tehran insisted it took place over Iranian airspace and said it was 'ready for war' as the U.S. heightened its rhetoric and warned it would respond in kind.

Trump said he would not take military action lightly in his first remarks on the topic. And he denied that he was being pushed to go to war by his advisers

'No no not at all. In fact in many cases it's the opposite,' he said. 'But I will say, look, I said I want to get out of these endless wars, I campaigned on that, I want to get out.'

He pointed to troop draw downs in Afghanistan, Iraq and Syria as evidence of his commitment to reduce America's military footprint.

'We beat the Caliphate. We took back the 100 percent of the Caliphate. At 99 percent, Justin, I said we're going to get out we're going to start peeling back and everybody went crazy because it was 99, and so I said all right, so we'll finish it up. So we got 100 per cent. And we're pulling that back out of Syria. We're pulling a lot of people back,' he contended.

Trump added, 'But this is a new wrinkle, a new fly in the ointment what happened, shooting down a drone. And this country will not stand for it, that I can tell you.'

He told a reporter who asked him about it as he was greeting Canadian PM Justin Trudeau outside the White House that the public would know soon about next steps.

'You'll soon find out,' he said in response to the shouted question.

A White House briefing at 3 pm ended without a new comment. Secretary of State Mike Pompeo and acting Defense Secretary Patrick Shanahan were seen leaving the White House an hour later.

Senior congressional leaders were briefed at 11 am. House Speaker Nancy Pelosi told reporters at her weekly press conference just beforehand, 'I don't think the president wants to go to war. There's no appetite for war in the country.'

'However we go forward, we have to realize that working together with our allies is very, very important,' she said.

In a statement after the briefings, Pelosi encouraged level-headed thinking.

'In light of the targeting of an unmanned U.S. drone by Iran, it is essential that we remain fully engaged with our allies, recognize that we are not dealing with a responsible adversary and do everything in our power to de-escalate,' she said.

'This is a dangerous, high-tension situation that requires a strong, smart and strategic, not reckless, approach.;

Allies of Iran and the United States were responding cautiously. France, Germany and the U.K. did not make statements immediately.

Israeli PM Bibi Netanyahu subsequently called on 'all peace-loving countries' to back Trump's effort to check Iranian aggression.

'In the last 24 hours, Iran has intensified its aggression against the United States and against all of us,' he said. 'Israel stands by the United States on this.'

Iranian commander Hossein Salami declared that his men are 'ready for war' and that the drone had been downed because 'borders are our red line'.

U.S. Navy Captain Bill Urban condemned the 'unprovoked attack,' adding that the 'Iranian reports that the aircraft was over Iran are false' in early comments.

The Islamic Republic News Agency, Iran's propaganda outlet, published a photograph purporting to show the burning aircraft falling from the sky, but the image was taken two years ago in Yemen.

Tehran said it destroyed an RQ-4 Global Hawk over the southern coastal province of Hormozgan. The U.S. initially said it was a Navy MQ-4C Triton in international airspace but confirmed later that it was indeed a Global Hawk. The two look similar and the Triton is a variant of the Global Hawk.

The downing of the drone is the latest example of how Iran is ramping up regional tensions with the U.S. after two tankers were hit by limpet mines last Thursday and four vessels were allegedly damaged by underwater drones in the Gulf last month.

Last week, the U.S. said Iran had attempted to strike another one of its drones which had circled above the stricken tankers.

A highly sophisticated missile will have been deployed to destroy the Navy spy plane (file photo), which will be deeply concerning to Washington not only for the weapons-capability of Tehran, but the secrets they could steal in examining the technology

The Islamic Republic News Agency, Iran's propaganda outlet, published this photograph purporting to show the burning aircraft falling from the sky, but the image was taken two years ago in Yemen

The US-made surveillance drone was brought down by Iran over the southern coastal province of Hormozgan, the Revolutionary Guard claimed

The Iranians claimed they had shot down a USAF RQ-4 Global Hawk (pictured), which the U.S. later confirmed

Iran claimed to have shot down an RQ-4 but the US confirmed a Navy MQ-4C was destroyed - the aircraft are visually similar and the MQ-4C is designed to replace the Navy's RQ-4s

The Triton could have only been downed by a sophisticated radar guided missile such as the Russian S-300 system which Iran operates (pictured: an S-300 missile is launched during Russian drills earlier this month)

The US Navy's MQ-4C Triton: The first few high-altitude, high-endurance Naval drones were introduced in May of last year. The U.S. plans to have a fleet of 68 operational by 2032. Capable of more than 30 hours at 56,000ft, Washington will be deeply concerned by the loss of the $180million drone. Not only does it signal sophisticated missiles exist in the Iranian arsenal, but also that their aeronautical technology may have fallen into Tehran's sinister hands. News that an MQ-4C was shot down has taken many by surprise because its first ever deployment was reportedly scheduled for this summer in the Pacific. The Triton was designed to replace the Navy's RQ-4 Global Hawks and are part of a generation of reconnaissance planes which have superseded the U-2 spy planes. The MQ-4C's optical/infrared (EO/IR) sensors enable full motion video surveillance with capabilities to detect, classify and track targets. It has Rolls-Royce engines, is 50ft long, with a wingspan of 130ft and a top speed of 368mph. Five crew members fly it from the ground and the drone feeds data back to bases in Florida and Washington. Advertisement

Salami, head of the Revolutionary Guard, announced Iran's borders 'represent our red line,' before a crowd in the western city of Sanandaj.

He told the people, 'Any enemy that violates the borders will be annihilated.'

Tehran's response to the drone was 'a clear message' from the 'defenders of the borders' of Iran, he told the Tasnim news agency.

Iran will 'respond to all foreign aggression and our reaction is, and will be, categorical and absolute.'

The drone went down just after 4am local time on Wednesday.

America and Tehran were already on a collision course. The U.S. blames Iran for the attacks on two oil tankers last week, which Tehran denies.

Commander Sean Kido of US Naval Forces Central Command, or NAVCENT, told reporters in the UAE yesterday that the limpet mine used in the attack on a Japanese-owned tanker 'is distinguishable and it is also strikingly bearing a resemblance to Iranian mines that have already been publicly displayed in Iranian military parades'.

The Japanese-owned Kokuka Courageous, loaded with highly flammable methanol, came under attack last Thursday as it passed through the Gulf of Oman along with the Norwegian-operated Front Altair.

Tehran has denied involvement and instead suggested Washington could be the author of the attacks, using the operation to justify force against Iran.

It was the second attack in a month on ships in strategic shipping lane.

On May 12, two Saudi oil tankers and two other vessels were damaged in mysterious 'sabotage attacks' in the Gulf of Oman off the United Arab Emirates.

The Japanese Kokuka Courageous off the coast of Fujairah in the UAE - it was attacked along with the Norwegian Front Altair in the Gulf of Oman last Thursday

Blast damage to the Kokuka Courageous after it was attacked in the Gulf of Oman last Thursday

Red handed? The Pentagon says this is a handprint from an individual who removed an unexploded limpet mine from the side of the Kokuka Courageous

An oil tanker is seen after it was attacked at the Gulf of Oman, in waters between Gulf Arab states and Iran on Thursday - Donald Trump has said the two attacks had Iran 'written all over it'

Kido said the US military had recovered 'biometric information' of the assailants on the Kokuka Courageous including fingerprints.

This information 'can be used to build a criminal case', Kido said as the US Navy took journalists to the damaged ship currently anchored some nine miles off Fujairah.

The relationship between Tehran and Washington has been particularly strained since the U.S. last year quit the Obama-era nuclear deal and reimposed sanctions.

The Americans have bolstered military presence in the Middle East and blacklisted Iran's Revolutionary Guards as a terrorist organisation.

Its deployment to the Gulf of an aircraft carrier as well as B-52 bombers, an amphibious assault ship and a missile defence battery has sparked fears of fresh conflict in the region.

Iran recently has quadrupled its production of low-enriched uranium and threatened to boost its enrichment closer to weapons-grade levels, trying to pressure Europe for new terms to the 2015 deal.

Mysterious attacks also have targeted oil tankers as Iranian-allied Houthi rebels launched bomb-laden drones into Saudi Arabia.

All this has raised fears that a miscalculation or further rise in tensions could push the U.S. and Iran into an open conflict, some 40 years after Tehran's Islamic Revolution.

This image released by the U.S. Department of Defense on Monday, June 17, 2019, and taken from a U.S. Navy helicopter, shows what the Navy says are members of the Islamic Revolutionary Guard Corps Navy removing an unexploded limpet mine from the M/T Kokuka Courageous

This grab taken from a video released by the US Central Command on June 13, 2019, reportedly shows an Iranian navy patrol boat in the Gulf of Oman approaching the Japanese operated methanol tanker Kokuka Courageous and removing an unexploded mine

Meanwhile, White House spokeswoman Sarah Sanders said Trump had been 'briefed on the reports of a missile strike in the Kingdom of Saudi Arabia.'

'We are closely monitoring the situation and continuing to consult with our partners and allies,' Sanders said.

The Houthi's Al-Masirah satellite news channel claimed the rebels targeted a power plant in Jizan, near the kingdom's border with Yemen, with a cruise missile. Saudi state media and officials did not immediately report a missile strike Thursday.

A Saudi-led coalition has been battling the Houthis since March 2015 in Yemen, the Arab world's poorest nation now pushed to the brink of famine by the conflict. In recent weeks, the Houthis have launched a new campaign sending missiles and bomb-laden drones into Saudi Arabia.