There are fears the attack on two oil tankers in the Middle East could lead to a major conflict between the United States and Iran.

The tankers were hit in suspected attacks in the Gulf of Oman and crews were evacuated, a month after a similar incident in which four tankers in the region were struck.

Overnight, US Secretary of State Mike Pompeo said the alleged attacks were part of a "campaign" of "escalating tension" by Iran and a threat to international peace and security.

Pompeo said there was strong evidence of Iran's culpability, after the US Navy said it had spotted an unexploded magnetic limpet mine stuck to the hull of one of the vessels.

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Two oil tankers near the strategic Strait of Hormuz were reportedly attacked on Thursday. Photo / AP
Two oil tankers near the strategic Strait of Hormuz were reportedly attacked on Thursday. Photo / AP

The US top diplomat said only Iran had the ability to undertake such an operation in that region, news.com.au reported.

"It is the assessment of the United States that the Islamic Republic of Iran is responsible for the attacks," Pompeo said.

"This is based on intelligence, the weapons used, the level of expertise needed to execute the operation, recent similar Iranian attacks on shipping, and the fact that no proxy group operating in the area has the resources and proficiency to act with such a high degree of sophistication."

United States government officials have now released video that reporetdly shows an Iranian navy boat removing an unexploded mine attached to the hull of the Japanese-owned chemical tanker attacked yesterday.

An oil tanker is on fire in the sea of Oman. Photo / AP
An oil tanker is on fire in the sea of Oman. Photo / AP

Officials said a US military aircraft overhead recorded the video of an Iranian boat moving alongside one of the stricken tankers and removing an unexploded limpet mine from its hull.

US defence officials believe the Iranians were trying to remove evidence of their role in the attack, CNN reports.

Pompeo speculated in his address this morning that Iran is "lashing out, because the regime wants our successful maximum pressure campaign lifted".

Iran itself has come out swinging in response to the claims, rejecting assertions they were behind the events on Thursday and similar attacks last month against four tankers on the same waterway.

In a strong statement, Iran's foreign minister Mohammad Javad Zarif, implied his nation had been framed.

"Suspicious doesn't begin to describe what likely transpired this morning," he wrote on Twitter.

Pompeo, hit back at the statement in his news conference — saying Zarif "may think this is funny, but no one else in the world does".

Two oil tankers near the strategic Strait of Hormuz were reportedly attacked on Thursday. Photo / AP
Two oil tankers near the strategic Strait of Hormuz were reportedly attacked on Thursday. Photo / AP

Russia was also quick to urge caution and officially denied the US accusations — saying no one should rush to conclusions about the incident or use it to put pressure on Tehran.

It comes as United Nations secretary general António Guterres expressed "deep concern" that the attack and subsequent blame game could lead to a major military escalation.

"Facts must be established, and responsibilities clarified," he urged in a speech to the Security Council. "If there is something the world cannot afford, it is a major confrontation in the Gulf region."

The two vessels were struck by explosions in the early daylight hours Thursday after leaving the Strait of Hormuz and traveling around 25 nautical miles off Iran's southern coast headed toward Asia.

The Norwegian-owned Front Altair ethanol tanker was hit by three explosions, according to the Norwegian Maritime Authority, and continued to burn late Thursday.

Explosions also struck the Japanese-owned Kokuka Courageous, which was loaded down with methanol, but the fire on board was soon extinguished.

There was no claim of responsibility for the blasts, which struck both tankers at the waterline.

Iran said its navy rescued several dozen crew members of the two vessels, while the US Navy said it had picked up 21 from the Kokuka Courageous.

The world's eyes are already firmly fixed on Iran this week, as Japanese Prime Minister Shinzo Abe is in Tehran for a state visit.

Sailors aboard the Arleigh Burke-class guided-missile destroyer USS Bainbridge render aid to the crew of the Kokuka Courageous. Photo / AP
Sailors aboard the Arleigh Burke-class guided-missile destroyer USS Bainbridge render aid to the crew of the Kokuka Courageous. Photo / AP

Abe explicitly urged Iran to avoid conflict at all costs, while pledging to do his utmost to ease tensions.

One the tankers damaged on Thursday is Japanese-owned — according Hiroshige Seko, Japan's minister of economy, trade and industry.

"This would seem very clumsy timing from a country (Iran) seeing the first tangible signs of any easing of the crippling sanctions imposed by the Americans," Bloomberg columnist Julian Lee wrote in an op-ed.

"But it is absolutely understandable if you're someone whose ultimate goal is to derail any easing of tensions between the two nations, and to effect regime change in Tehran. Whoever is behind the attacks is no friend of Iran."

RISING US AND IRAN TENSIONS

Tensions between the US and Iran have been rising since President Donald Trump pulled out of Barack Obama's nuclear deal last year, which traded sanctions relief for certain curbs on the regime's nuclear weapons program.

The two sides have fought for years through proxy forces in Middle Eastern countries including Lebanon, Iraq, Syria and Bahrain.

In Yemen, this conflict has had devastating consequences for more than four years as Saudi and Emirati — backed with US bombs — forces try to take back control of the nation from Houthi rebels aligned with Iran.

The conflict has pushed 14 million people to the brink of starving to death.

The war of words between Iran and the US has spiked in recent weeks, with Trump posting strongly-worded tweets in response to perceived threats from Tehran.

"If Iran wants to fight, that will be the official end of Iran," he wrote on May 19. "Never threaten the United States again!"

The attacks on oil tankers has served to inflame the sabre-rattling rhetoric as they have taken place near the entrance to the Strait of Hormuz — a crucial shipping artery for Saudi Arabia, the world's biggest oil exporter, and other Gulf energy producers.

The shipping lane is used to move one-fifth of the world's oil supply and is critical to the world's economy.

Iran's navy rescued 44 crew members from the two oil tankers which caught fire after what was reported as an "accident", official news service Islamic Republic News Agency reported.

"Forty-four sailors from the two foreign oil tankers which had an accident this morning in the Sea of Oman were saved from the water by the (navy) rescue unit of Hormozgan province and transferred to the port of Bandar-e-Jask," IRNA quoted an "informed source" as saying.

The attack yesterday has caused crude oil prices to skyrocket.

Benchmark Brent crude oil spiked at one point by as much for per cent in trading following the reported attack, to over $US62 ($95) a barrel, highlighting how crucial the area remains to global energy supplies.