The United States accused Iran of carrying out attacks that left two tankers ablaze in the Gulf of Oman on Thursday, escalating tensions across the region and sending world oil prices soaring.

The U.S. military released a  video late on Thursday that it said showed Iran's Revolutionary  Guard (IRGC) removing an unexploded mine from the side of a  Japanese-owned oil tanker.

The U.S. military's Central Command also released photographs showing the apparent mine, which attaches to the  side of a ship magnetically, before it was removed later in the day. 

Secretary of State Mike Pompeo warned that Washington will defend its forces and allies in the region, and the United States pressed its case as the UN Security Council met to address the incident – the second in a month in the strategic sea lane.  

With tensions spiraling between Iran and the United States, the European Union called for "maximum restraint" as UN chief Antonio Guterres warned the world cannot afford a major confrontation in the Gulf.

Iran labeled the apparent attacks as "suspicious," as its Supreme Leader Ayatollah Ali Khamenei rebuffed overtures by visiting Japanese leader Shinzo Abe to open talks with U.S. President Donald Trump.  

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

The U.S. top diplomat said that in region only Iran had the ability to undertake such an operation. "It is the assessment of the United States that the Islamic Republic of Iran is responsible for the attacks," Pompeo announced.  

"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," he said.  

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 U.S. Navy said it had picked up 21 from the Kokuka Courageous.  

Pompeo called Thursday's tanker explosions "the latest in a series of attacks" he alleged were undertaken by Iran or its "proxies," including, he said, a missile attack against a southern Saudi Arabia airport by the Iran-aligned Huthis in Yemen on Wednesday. 

The latest incident came as Abe was on an unprecedented visit to Tehran, seeking to defuse tensions. 

"It is essential that Iran plays a constructive role in building solid peace and stability in the Middle East," Abe told a joint news conference with Iran's President Hassan Rouhani.  

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Japanese ship among tankers attacked near Strait of Hormuz: Tokyo

"Today, tension is rising in the Middle East. Some experts point out that the conflict might be triggered accidentally," he said. 

Supreme Leader Khamenei rejected Abe's overture, saying: "We have no doubt in your goodwill and seriousness, but regarding what you said the U.S. president told you, I don't consider Trump as a person worthy of exchanging messages with."  

But Trump dismissed the idea of early talks. "I personally feel that it is too soon to even think about making a deal. They are not ready, and neither are we!" he tweeted.