Thursday’s attack came one month after Iranian forces allegedly used naval mines to blow holes in two oil tankers and two smaller ships off the Emirati port of Fujairah. The US publicly said Iran was behind the attack, and pointed to similarities with yesterday's attack, while Tehran denied responsibility.

Javad Zarif, the Iranian foreign minister, said “suspicious doesn’t begin to describe” the incident in Gulf of Oman. He previously suggested without evidence that Israel was staging the attacks to undermine Iran.

Responding to Mr Zarif's comments, Mr Pompeo said: " Foreign Minister Zarif may think this is funny but no one else in the world does."

The explosions at sea came hours before Shinzo Abe, Japan’s prime minister, met with Ayatollah Khamenei, the supreme leader of Iran, on a diplomatic mission intended to try to ease tensions between Iran and the US. But the Japanese leader’s efforts appeared to bear little fruit.

Ayatollah Khamenei refused to hear any messages from Donald Trump delivered by Mr Abe, the Iranian government said.

The ayatollah also said Iran was not seeking nuclear weapons but “America could not do anything” to stop Tehran if it did decide to pursue a nuclear course.

Pictures on board an oil tanker (left, top right) shows it billowing black smoke, which can be seen from afar (bottom right) credit: Fars News Agency/AP

Both tankers were carrying “Japanese-related” cargo, according to Japan’s government.

It was not clear if that was a coincidence or if the targeting of the ships was done deliberately to coincide with Mr Abe’s visit to Tehran.

While Iran’s civilian government denies responsibility for any of the attacks, it is possible that the Revolutionary Guard, who answer directly to the supreme leader, are carrying out operations without the government’s knowledge or consent.

Iran tries to keep tensions between the two sides concealed but they spilled into the open early this year when Mr Zarif threatened to resign after he was left out of a key meeting while a senior Revolutionary Guard commander was invited.

The attacks capped six weeks of building tensions between Iran and the US during which time Mr Trump has ordered an aircraft carrier, a bomber taskforce and 1,500 additional troops to the Middle East.

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Both the US and Iran say they are not looking for war but Britain and other countries have warned of the danger that the two sides could stumble into an unintended conflict.

Antonio Gutteres, the UN secretary general, condemned the attack and warned that the world cannot afford “a major confrontation in the Gulf region”.

Any fighting near the Strait of Hormuz, the waterway which transports 20 per cent of the world’s oil, would likely cause serious damage to global energy supplies.

Analysts said that Iran appeared to be lashing out in order to send a message in response to crippling US sanctions imposed by Mr Trump after he withdrew the US from the 2015 nuclear deal.

“I think Iran is showing that it has teeth,” said Charles Hollis, a former British diplomat in Tehran who is now managing director of the Falanx Assynt consultancy. “It’s a way of showing that if they are backed into a corner they are not without means of causing grief.”

Details of the attack remained sketchy but the crew of the Front Altair reported reported hearing three explosions. Aerial footage from Iranian state television showed a fire raging on the starboard side of the ship while the rear also appeared damaged and blackened.

Shinzo Abe met the Supreme Leader of Iran, Ali Khamenei during his official visit in Tehran, and Iranian President Hassan Rouhani credit: IRANIAN SUPREME LEADER PRESS OFFICE - HANDOUT/Anadolu Agency/Getty Images

The ship was “suspected of being hit by a torpedo”, according to Taiwan’s state-owned petrol company. The second tanker, Kokuka Courageous, was damaged in a "suspected attack" that breached the hull above the water line while on passage from Saudi Arabia to Singapore, according to Bernhard Schulte Ship management.

Oil prices rose more than 4 per cent in response to Thursday’s explosions, the strongest surge in five months. Prices later came down to around 2 per cent above their opening level and overall prices remain lower than they were a month ago.

“This is a fairly small increase given the uncertainty and the potential knock-on effects of attacks such as these,” said Cailin Birch, global economist at The Economist Intelligence Unit.

She said markets had to some extent already factored in instability in the Gulf after the hostilities of recent weeks. Iran has warned that it will begin enriching high-grade uranium, the kind that could be used for a nuclear weapon, in July unless Europe finds a way to get around US sanctions and prop up the Iranian oil and banking sectors.

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Such a move would be a violation of the 2015 nuclear agreement and the EU has warned Iran not to take this step. Britain, France, and Germany have defied the US by building a financial vehicle designed to circumvent American sanctions and allow trade with Iran.

But so far there is little sign that businesses are prepared to risk getting caught in US sanctions by using vehicle, known as Instex. Heiko Mass, Germany’s foreign minister, visited Tehran earlier this week to urge the Iranians not to violate the nuclear agreement.

He said it was in Iran’s “political and strategic interest to maintain this agreement and the dialogue with Europe”. Iran accused the European states of failing to live up to their commitments.

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07:55PM Trump: It is too soon to even think about a deal

While Mike Pompeo was speaking, Donald Trump tweeted to say it's "too soon" to consider making a deal with Iran.

He wrote: "While I very much appreciate P.M. Abe going to Iran to meet with Ayatollah Ali Khamenei, I personally feel that it is too soon to even think about making a deal. They are not ready, and neither are we!"

07:26PM US blames Iran for oil tanker attacks

Mike Pompeo, the US Secretary of State, said that America believes Iran is responsible for the attacks on tankers in the Gulf of Oman.

Mr Pompeo said the assessment was based on intelligence, the type of weapons used and the level of sophistication of the assaults.

05:16PM Analysis: Anti-Iran hawks will not necessarily see the attacks as a bad thing

Roland Oliphant, Senior Foreign Correspondent writes:

Iran hawks will almost certainly blame today's attacks on oil tankers on Iran. But that doesn't mean they will see the attacks as a bad thing.

On the contrary, they are likely to argue that it shows their hard line on Iran is working.

Donald Trump's White House has pursued a campaign of "maximum" economic pressure on Iran since pulling out of the 2015 nuclear deal - also called the Joint Comprehensive Plan of Action (JCPOA) one year ago.

The idea - championed by US National Security Advisor John Bolton and Israeli prime minister Benjamin Netanyahu - is to make economic life so difficult that the regime in Tehran is forced to return to accept even more restrictive conditions. And the policy has indeed had a serious impact inside the country.

So when Iran announced it would suspend some of its commitments under the deal in protest last month, it was read in those circles as a signal that Hassan Rouhani's government is feeling the pressure.

And the May 12 attacks on four tankers days later were read as Iran's way of signalling its deep unhappiness with the status quo, without hitting the threshold of all out war.

Today's attacks also appear to fit that pattern: the explosions may have been more spectacular than the May incident, but they also avoided actually sinking the ships or killing anyone.

So expect the hawks to argue that Iran is hitting out because it is desperate, and that now is not the time to blink.

Not everyone will be reassured by such an analysis. After all, no evidence that Iran was involved in either attack has been presented in public.

And even countries that share US concerns about Iran's actions in the region, including the United Kingdom, disagree profoundly with Mr Trump about the best way to change Tehran's behaviour.

04:49PM How the Strait of Hormuz became a tinder box choke point in the proxy conflicts of the Middle East

Adrian Blomfield writes: "There is arguably no more strategic, nor more vulnerable, waterway in the world. Even the United States calls the Strait of Hormuz 'the world’s most important chokepoint.'" Click here for detailed analysis.

03:29PM The 'strange' Iranian claims

Iranian state media reported earlier that 44 sailors from the two oil tankers had been rescued and taken to Hormozgan in southern Iran, The Telegraph's Middle East Correspondent reports.

That seemed a little strange given that the crew of one of the tankers was evacuated onto a cargo ship linked to the UAE. Why would a UAE ship drop the sailors in Iran?

The US Navy is now contradicting the Iranian report and says that 21 of the rescued sailors are onboard the USS Bainbridge, an American missile destroyer that was in the area at the time.

US officers are likely speaking to the rescued crew and trying to understand what happened to the oil tanker.

03:02PM Highly likely Iran caused attacks'

Just like a month ago, the US has pointed the finger at Tehran with regards to the suspected attack in the Gulf of Oman.

A US defence official told CBS News' senior national security correspondent David Martin it was "highly likely Iran caused these attacks".

Iran claimed to have rescued the crews of both vessels on Thursday, but the Pentagon official dismissed this version of events as "patently false."

The USS Bainbridge picked up 21 crew members, the official said.

02:38PM Timeline of recent US-Iran events

May 5: John Bolton, the White House national security adviser and a longtime Iran hawk, announces the deployment of the USS Abraham Lincoln carrier strike group and a bomber task force in response to "a number of troubling and escalatory indications and warnings," without providing details. He threatens "unrelenting force" in response to any attack.

May 8: Iran vows to enrich its uranium stockpile closer to weapons-grade levels starting July 7 if world powers fail to negotiate new terms for its nuclear deal. The US responds by imposing sanctions on Iran's metals industry.

May 9: The European Union urges Iran to respect the nuclear deal and says it plans to continue trading with the country despite US sanctions. Trump says he would like Iran's leaders to "call me."

May 10: The US says it will move a Patriot missile battery into the Middle East to counter threats from Iran.

May 12: The United Arab Emirates says four commercial ships off its eastern coast "were subjected to sabotage operations," just hours after Iranian and Lebanese media outlets air false reports of explosions at a nearby Emirati port.

May 13: European foreign ministers urge the United States and Iran to show restraint, while Secretary of State Mike Pompeo briefs his counterparts on the alleged threats from Iran. Trump warns that if Tehran does "anything" in the form of an attack "they will suffer greatly."

May 14: Yemen's Iran-aligned Houthi rebels launch a drone attack on Saudi Arabia, striking a major oil pipeline and taking it out of service.

The New York Times reports the White House is reviewing military plans that could result in sending 120,000 US troops to the Middle East if Iran attacks American forces or steps up work on nuclear weapons. Trump says it's "fake news," but that he would "absolutely" be willing to send troops if necessary.

Iran's Supreme Leader Ayatollah Ali Khamenei says "no one is seeking war," but that it wouldn't be difficult for Iran to enrich uranium to weapons-grade levels.

A senior military officer in the US-backed coalition fighting the Islamic State group says "there's been no increased threat from Iranian-backed forces in Iraq and Syria." In a rare public rebuttal, US Central Command says his remarks "run counter to the identified credible threats."

May 15: The US Embassy in Baghdad orders all nonessential government staff to leave Iraq immediately. The Netherlands and Germany say they are suspending their training of Iraqi forces.

May 16: Saudi Arabia blames Iran for the drone attack on its pipeline and an English-language newspaper close to the palace calls for the US to launch "surgical" strikes in retaliation.

President Donald Trump says he hopes the US is not on a path to war with Iran amid fears that his two most hawkish advisers could be angling for a conflict with the Islamic Republic. Asked if the US was going to war with Iran, the president replied, "I hope not" - a day after he repeated a desire for dialogue, tweeting, "I'm sure that Iran will want to talk soon."

May 19: A rocket lands near the US Embassy in Baghdad, without harming anyone. It's not clear who is behind the attack, but after the initial reports, Trump tweets: "If Iran wants to fight, that will be the official end of Iran. Never threaten the United States again!" Iran's foreign minister responded by tweeting that Trump had been "goaded" into "genocidal taunts."

May 20: Semi-official media in Iran report that it has quadrupled its production of low-enriched uranium, which is used for civilian applications but not nuclear weapons. Iran is allowed to enrich uranium to the low level of 3.67%, but increased production could lead it to exceed the stockpile limits in the nuclear deal.

May 24: President Donald Trump says the US will bolster its military presence in the Middle East with an additional 1,500 troops. He says the troops will have a "mostly protective" role.

- Senior Pentagon officer Vice Admiral Michael Gilday says the U.S. has a high degree of confidence that Iran's Revolutionary Guard was responsible for the explosions of the four tankers in the Gulf of Oman, and that Iranian proxies in Iraq fired rockets into Baghdad.

May 31 and June 1: Saudi Arabia's King Salman hosts three high-level summits in Mecca, drawing heads of state from across the Middle East and Muslim countries to present a unified Muslim and Arab position on Iran. The monarch calls on the international community to use all means to confront Iran and accuses the Shiite power of being behind "terrorist operations" that targeted Saudi oil interests.

June 12: Saudi Arabia says 26 people were wounded in an attack by Yemen's Houthi rebels targeting an airport in kingdom's southwestern town of Abha. The Houthis claim they'd launched a cruise missile at the airport.

June 13: Two oil tankers near the strategic Strait of Hormuz were reportedly attacked in an assault that left one ablaze and adrift as 44 sailors were evacuated from both vessels and the US Navy rushed to assist.

01:32PM Oil supply to entire Western world 'could be at risk'

The chairman of the Intertanko Tanker Association has issued a stark warning in the aftermath of the suspected attacks.

Paolo d’Amico said: "We need to remember that some 30% of the world’s (seaborne) crude oil passes through the Straits.

"If the waters are becoming unsafe, the supply to the entire Western world could be at risk."

Meanwhile oil tanker owners DHT Holdings and Heidmar have reportedly suspended bookings to the Arab Gulf, according to Marc Ostwold, Chief Economist/Strategist at ADM Investor Services International Ltd, quoting ship brokers.

01:20PM Dramatic video footage of burning tanker

The Telegraph's Middle East Correspondent Raf Sanchez has obtained this dramatic footage showing a tanker on fire.

Watch it here:

12:51PM White House 'aware' and 'addressing situation'

Donald Trump has been on Twitter this morning, but has not mentioned the incident in the Gulf.

Instead, he went on an earl-morning rant bashing the Democrats.

But Sarah Huckabee Sanders has talked to Al Arabyia, and said: "We are aware of the reports of an attack on ships in the Gulf of Oman and we are assessing the situation.

12:32PM First pictures from on board burning tanker emerge

The fire rages on board one of the tankers credit: Fars News Agency

Black smoke billows skywards credit: Fars News Agency

12:09PM More tanker pictures emerge

The Iranian Students' News Agency (ISNA) has released aerial shots of what it claims to be the "attacked" tanker in the Gulf of Oman.

This picture, obtained by AFP from Iranian State TV IRIB, reportedly shows smoke billowing from a tanker said to have been attacked off the coast of Oman, at an undisclosed location.

This picture, obtained by AFP from Iranian State TV IRIB, reportedly shows smoke billowing from a tanker credit: IRIB/AFP

11:56AM The suspected attacks, in graphics

The Telegraph's graphics team have pulled together this map explaining the latest development.

View more!

And here is a slightly different take on it:

11:40AM No 10: 'UK urgently seeking to establish facts'

The UK is urgently seeking to establish the facts, the prime minister's spokesman told Sky News.

11:31AM The meaning behind that tweet from Iranian Foreign Minister

Our Middle East Correspondent Raf Sanchez has dissected that incredible tweet by Iran's Foreign Minister.

Javad Zarif, Iran’s foreign minister, has just tweeted saying that “suspicious doesn’t begin to describe what likely transpired this morning” in the Gulf of Oman.

He notes that the attack happened on the same day that Abe Shinzo, the Japanese prime minister, was meeting with Iran’s supreme leader “for extensive and friendly talks”. Mr Zarif doesn’t say it explicitly but his implication is clear: he is suggesting that someone staged the attack to put blame on Iran and scupper the Japanese diplomatic visit. Last month, Mr Zarif pointed the finger at Mossad, the Israeli intelligence agency, and accused them of “fabricating intelligence about Iran’s involvement” in the May 12 attack at Fujairah.

The reality is that Mr Zarif is part of the civilian government of Iran, which has no control over the Revolutionary Guard, who report directly to the supreme leader. It is quite possible that the Revolutionary Guard could carry out attacks and Mr Zarif would not know about it. Or that he would know but be powerless to stop them. Iran works hard to try to hide internal tensions between the civilian government and the Revolutionary Guard. But those tensions spilled into the open in March when Mr Zarif was left out of a meeting with Bashar al-Assad, the Syrian leader. His seat in the meeting was taken by Qasem Soleimani, a senior Revolutionary Guard commander. An incensed Mr Zarif tried to resign but his resignation was not accepted by the Iranian president and he eventually returned to his post.

11:08AM Iran: 'Suspicious doesn't begin to describe what likely transpired this morning'

Iran's Foreign Minister has described the suspected attack on Thursday morning as "suspicious".

In a tweet, published in English, he said:

11:01AM Tanker firm denies vessel has sunk

Frontline’s Front Altair oil tanker is still on fire in the Gulf of Oman and has not sunk, a spokesman for the company said on Thursday, citing information from a nearby vessel.

Earlier, both Israeli and Iranian state media had reported the tanker was sinking.

Separately, the ship’s technical operator, International Tanker Management, said the cause of the explosion was still unknown.

10:50AM Another photograph emerges of tanker fire

Al Hadath - an Arabic weekly newspaper based in Amman, Jordan - has released a photograph showing one of the tankers on fire.

A fire on one of the two carriers in the Gulf of Oman credit: Al Hadath

10:47AM Map of tankers in the Gulf of Oman

These are the last known locations of the two tankers - the Norwegian-owned Front Altair and the Kokuka Courageous.

Map of tankers credit: Reuters

10:39AM Britain 'deeply concerned' by reports of suspected attack

Britain said on Thursday it was deeply concerned by reports of explosions and fires on vessels in the Strait of Hormuz.

Shipping firms and industry sources said two oil tankers were hit in suspected attacks in the Gulf of Oman and the crews have been evacuated, a month after a similar incident in which four tankers in the region were struck.

“We are deeply concerned by reports of explosions and fires on vessels in the Strait of Hormuz. We are in contact with local authorities and partners in the region,” a British government spokeswoman said.

10:28AM Tehran will 'in no way repeat' negotiations with US

Iran’s Supreme Leader Ayatollah Ali Khamenei says that Tehran "will in no way repeat" negotiations with the US amid tension over its unraveling nuclear deal with world powers.

Khamenei made the comment on Thursday during a meeting with Japanese Prime Minister Shinzo Abe who traveled to Tehran as an interlocutor for President Donald Trump to ease tensions between Washington and Tehran.

Iran's Supreme Leader Ayatollah Ali Khamenei meets with Japan's Prime Minister Shinzo Abe in Tehran credit: Reuters

But the comments by Khamenei could indicate that Abe’s visit may not have succeeded.

Khamenei’s official website quoted him as telling Abe: "I don’t regard Trump as deserving any exchange of messages and have no response for him and will give no response."

Khameneni also said that while Tehran doesn’t want an atomic bomb, “America could not do anything” to stop Iran if it did.

10:26AM Tankers were carrying 'Japan-related' cargo

Japan’s Trade Ministry says the two oil tankers reportedly attacked near the Strait of Hormuz carried “Japan-related” cargo.

Thursday’s comment came as Japanese Prime Minister Shinzo Abe was wrapping up a two-day trip to Iran with a mission to ease tensions between Tehran and Washington.

No one has claimed responsibility or explained how the tankers were attacked. However, the US previously blamed Iran for an attack last month on four oil tankers close to the nearby Emirati port of Fujairah.

10:13AM Tanker pictured on fire in Gulf

This picture from the Iranian Student News Agency (ISNA) shows one of the tankers hit by the suspected attack on fire in the Gulf of Oman.

10:01AM The background of US-Iran bad blood

The US has been building up forces in the Middle East since early May, when the White House said it had evidence that Iran was preparing attacks against American troops in the region, writes Raf Sanchez.

US intelligence agencies were alarmed by photographs or Iranian forces loading armed missiles onto small boats in the Persian Gulf.

US intelligence also reportedly picked up evidence that Iran had activated Shia militias in Iraq to carry out attacks against American forces and diplomatic facilities.

Since then the US has sent an aircraft carrier, 1,500 additional troops, a bomber task force and several batteries of missile interceptors to the region.

Donald Trump has repeatedly said he is not looking to provoke a war with Iran but the UK and other allies fear that the two sides could stumble into an unintended conflict.

Meanwhile, Shinzo Abe, the prime minister of Japan, is visiting Iran. The trip is officially commemorating 90 years of diplomatic relations between Iran and Japan but Mr Abe has also said he is eager to try to calm tensions between the two sides.

09:58AM US Navy response

A US Navy spokesman said: "We are aware of the reported attack on shipping vessels in the Gulf of Oman.

"US Naval Forces in the region received two separate distress calls at 6.12am local (Bahrain) time and a second one at 7am US Navy ships are in the area and are rendering assistance."

09:56AM Almost 50 crew taken to Iranian port

Forty-four crew members from two tankers involved in an incident near the Strait of Hormuz have been taken to an Iranian port, according to Iran state TV.

09:55AM First picture of tanker emerges

A Saudi news outlet has claimed to have obtained the first photograph of one of the tankers hit by a suspected attack in the Gulf of Oman.

Watch the Saudi news report here:

09:51AM One of the oil tankers 'sinks'

One of the two oil tankers hit by explosions in a suspected attack has sunk, according to reports.

Kann - the public broadcaster in Israel - said that the vessel had gone underwater, but that the crew had been saved.

09:44AM Surge in oil prices after 'suspected attack'

Oil prices have bounced back from a five-month low after a suspected attack on two oil tankers in the Sea of Oman as geopolitical tensions simmer in the region, writes Tom Rees from our Business Desk.

Price suddenly surged after the US Navy revealed that two tankers were damaged near the Strait of Hormuz, a crucial waterway that transports a fifth of the world's oil.

View more!

Iran has threatened to close the Strait of Hormuz after its oil exports were hit by American sanctions and the latest incident in the region comes shortly after two Saudi tankers were sabotaged in an attack the US has blamed on Tehran.

Prices slumped yesterday after another unexpected rise in US crude stockpiles compounded fears of stuttering demand. The rise in tensions helped oil stage a recovery as prices surged as much as 4.5pc to above $62 per barrel in its biggest intraday jump in five months.