Two oil tankers near the strategic Strait of Hormuz were damaged in suspected attacks on Thursday, leaving one ablaze and the other adrift and forcing sailors to evacuate in the latest mysterious incident involving tankers amid heightened tensions between the U.S and Iran.

The U.S. Navy, which rushed in to assist the stricken vessels, and the ship’s owners offered no immediate explanation on what weapon caused the damage to the MT Front Altair and the Kokuka Courageous in the Gulf of Oman off the coast of Iran, though all believed the ships had been targeted in an attack. The Front Altair burned for hours afterward, charring half of one of the vessel’s sides and sending thick black smoke into the sky.

Last month, the U.S. alleged that Iran used limpet mines to attack four oil tankers off the nearby Emirati port of Fujairah. Iran denied being involved, but the incidents came as Iranian-backed rebels in Yemen also have launched missile and drone attacks on Saudi Arabia, including on oil infrastructure.

In this photo released by state-run IRIB News Agency, an oil tanker is on fire in the sea of Oman, Thursday, June 13, 2019. Two oil tankers near the strategic Strait of Hormuz have been reportedly attacked. The alleged assault on Thursday left one ablaze and adrift as sailors were evacuated from both vessels. The U.S. Navy rushed to assist amid heightened tensions between Washington and Tehran. (IRIB News Agency via AP)
In this photo released by state-run IRIB News Agency, an oil tanker is on fire in the sea of Oman, Thursday, June 13, 2019. (IRIB News Agency via AP)

Meanwhile in Iran, Supreme Leader Ayatollah Ali Khamenei warned that while Tehran doesn’t seek nuclear weapons, “America could not do anything” to stop Iran if it did.

The comments came during a one-on-one meeting capping Japanese Prime Minister Shinzo Abe’s high-stakes visit in Tehran that sought to ease Iran-U.S. tensions, suggested the efforts had failed.

In this photo released by state-run IRIB News Agency, an oil tanker is on fire in the sea of Oman, Thursday, June 13, 2019. Two oil tankers near the strategic Strait of Hormuz have been reportedly attacked. The alleged assault on Thursday left one ablaze and adrift as sailors were evacuated from both vessels. The U.S. Navy rushed to assist amid heightened tensions between Washington and Tehran. (IRIB News Agency via AP)
In this photo released by state-run IRIB News Agency, an oil tanker is on fire in the sea of Oman, Thursday, June 13, 2019. (IRIB News Agency via AP)

Benchmark Brent crude spiked at one point by as much 4% in trading following the suspected attack, to over $62 a barrel, highlighting how crucial the area remains to global energy supplies. A third of all oil traded by sea passes through the strait, which is the narrow mouth of the Persian Gulf.

Cmdr. Joshua Frey, a 5th Fleet spokesman, said the U.S. Navy was assisting the two vessels that he described as being hit in a “reported attack.” He did not say how the ships were attacked or who was suspected of being behind the assault. The American destroyer USS Bainbridge was sent to assist, he said.

The MT Front Altair, a Marshall Islands-flagged crude oil tanker, immediately caught fire after the suspected attack.

This May 2018 image made available by Marine Traffic shows the MT Front Altair in Antwerp, Belgium. Two oil tankers near the strategic Strait of Hormuz were reportedly attacked on Thursday June 13, 2019. International Tanker Management, which operates the MT Front Altair, said an explosion caused fire aboard but that the incident is still being investigated. (Patrick Vereecke/Marine Traffic via AP)
This May 2018 image made available by Marine Traffic shows the MT Front Altair in Antwerp, Belgium. (Patrick Vereecke/Marine Traffic via AP)

The firm that operates the Front Altair told The Associated Press that an explosion was the cause of the fire onboard. Its crew of 23 is safe after being evacuated by the nearby Hyundai Dubai vessel, it said.

BSM Ship Management said the Kokuka Courageous sustained hull damage and 21 sailors had been evacuated, with one suffering minor injuries.

Iranian state television said 44 sailors from the two tankers have been transferred to an Iranian port in the southern province of Hormozgan.

Michio Yube, right, director and general manager at the Kikuka Sankyo Co., LTD., speaks to media after one of their ships, the Kokuka Courageous, was attacked near the Strait of Hormuz, at Kikuka Sankyo Co., LTD. Thursday, June 13, 2019, in Tokyo. Two oil tankers near the strategic Strait of Hormuz were reportedly attacked on Thursday, an assault that left one ablaze and adrift as sailors were evacuated from both vessels and the U.S. Navy rushed to assist amid heightened tensions between Washington and Tehran. (AP Photo/Eugene Hoshiko)
Michio Yube, right, director and general manager at the Kikuka Sankyo Co., LTD., speaks to media after one of their ships, the Kokuka Courageous, was attacked near the Strait of Hormuz, at Kikuka Sankyo Co., LTD. Thursday, June 13, 2019, in Tokyo. (AP Photo/Eugene Hoshiko)

The Front Altair came from Ruwais in the UAE, a loading point for the state-run Abu Dhabi National Oil Co., according to the data firm Refinitiv. It carried naphtha, a flammable hydrocarbon. The Kokuka Courageous, came from Mesaieed, Qatar, and Jubail, Saudi Arabia, carrying methanol, a chemical compound used in a variety of products, Refinitiv said.

The fact that both vessels remained afloat suggested mines may have damaged them, said Jakob P. Larsen, head of maritime security for BIMCO, the largest international association representing ship owners.

“Judging from the damage, it doesn’t look like a torpedo, it looks like something smaller, whether that is a vessel-borne improvised explosive device or even a limpet mine,” he told the AP.

A security guard stand guard in front of Kikuka Sankyo Co., LTD, owner of the Kokuka Courageous, which was attacked near the Strait of Hormuz, Thursday, June 13, 2019, in Tokyo. (AP Photo/Eugene Hoshiko)
A security guard stand guard in front of Kikuka Sankyo Co., LTD, owner of the Kokuka Courageous, which was attacked near the Strait of Hormuz, Thursday, June 13, 2019, in Tokyo. (AP Photo/Eugene Hoshiko)

He added: “The shipping industry views this as an escalation of the situation, and we are just about as close to a conflict without there being an actual armed conflict, so the tensions are very high.”

The timing of Thursday’s suspected attack was especially sensitive as Abe’s high-stakes diplomacy mission was underway in Iran. Japan’s Trade Ministry said the two vessels had “Japan-related cargo,” without elaborating.

On Wednesday, after talks with Iranian President Hassan Rouhani, Abe warned that any “accidental conflict” that could be sparked amid the heightened U.S.-Iran tensions must be avoided.

A journalist photographs a picture of the Kokuka Courageous, which was attacked near the Strait of Hormuz, at the Kikuka Sankyo Co., LTD office, owner of the Kokuka Courageous, Thursday, June 13, 2019, in Tokyo. (AP Photo/Eugene Hoshiko)
A journalist photographs a picture of the Kokuka Courageous, which was attacked near the Strait of Hormuz, at the Kikuka Sankyo Co., LTD office, owner of the Kokuka Courageous, Thursday, June 13, 2019, in Tokyo. (AP Photo/Eugene Hoshiko)

His message came just hours after Yemen’s Iranian-backed Houthi rebels attacked a Saudi airport, striking its arrivals hall before dawn and wounding 26 people Wednesday. A Saudi-led coalition has been fighting for over four years against the Houthis, whom United Nations experts and the West say receive arms from Iran. Tehran denies that.

A statement published by Khamenei’s website after Abe’s meeting Thursday with the supreme leader suggested a tense exchange between the two.

“We have no doubt about your good will and seriousness, but … I don’t regard (President Donald) Trump as deserving any exchange of messages,” Khamenei reportedly told Abe.

This undated photograph from the United Arab Emirates' Mission to the United Nations released Thursday, June 6, 2019, shows the damage done to the Emirati-owned oil tanker A. Michel off the coast of Fujairah, United Arab Emirates. A joint statement released Thursday by Saudi Arabia, the UAE and Norway said the damage done to the four oil tankers off the UAE likely came from limpet mines placed by a
This undated photograph from the United Arab Emirates’ Mission to the United Nations released Thursday, June 6, 2019, shows the damage done to the Emirati-owned oil tanker A. Michel off the coast of Fujairah, United Arab Emirates. (United Arab Emirates’ Mission to the United Nations via AP)

Khamenei also said Iran remained opposed to building atomic weapons, but offered a challenge to Trump.

“You should know that if we planned to produce nuclear weapons, America could not do anything,” said Khamenei, who has final say on all matters of state in Iran’s Shiite theocracy.

Tensions have escalated in the Mideast as Iran appears poised to break the 2015 nuclear deal with world powers, an accord that the Trump administration pulled out of last year.

In this picture released by an official website of the office of the Iranian supreme leader, Supreme Leader Ayatollah Ali Khamenei, right, meets with Japanese Prime Minister Shinzo Abe, in Tehran, Iran, Thursday, June 13, 2019. A portrait of the late Iranian revolutionary founder Ayatollah Khomeini hangs on the wall. (Office of the Iranian Supreme Leader via AP)
In this picture released by an official website of the office of the Iranian supreme leader, Supreme Leader Ayatollah Ali Khamenei, right, meets with Japanese Prime Minister Shinzo Abe, in Tehran, Iran, Thursday, June 13, 2019. (Office of the Iranian Supreme Leader via AP)

Iran’s nuclear deal saw Tehran agree to limit its enrichment of uranium in exchange for the lifting of crippling sanctions.

In withdrawing from the deal last year, Trump pointed to the accord not limiting Iran’s ballistic missile program and not addressing what American officials describe as Tehran’s malign influence across the wider Middle East. Those who struck the deal at the time described it as a building block toward further negotiations with Iran, whose Islamic government has had a tense relationship with America since the 1979 takeover of the U.S. Embassy in Tehran and subsequent hostage crisis.

Already, Iran says it quadrupled its production of low-enriched uranium. Meanwhile, U.S. sanctions have cut off opportunities for Iran to trade its excess uranium and heavy water abroad, putting Tehran on course to violate terms of the nuclear deal regardless.

Japanese Prime Minister Shinzo Abe, left, and Iranian President Hassan Rouhani shake hands after their joint press conference at the Saadabad Palace in Tehran, Iran, Wednesday, June 12, 2019. The Japanese leader is in Tehran on an mission to calm tensions between the U.S. and Iran. (AP Photo/Ebrahim Noroozi)
Japanese Prime Minister Shinzo Abe, left, and Iranian President Hassan Rouhani shake hands after their joint press conference at the Saadabad Palace in Tehran, Iran, Wednesday, June 12, 2019. The Japanese leader is in Tehran on an mission to calm tensions between the U.S. and Iran. (AP Photo/Ebrahim Noroozi)
In this picture released by the official website of the office of the Iranian supreme leader, Supreme Leader Ayatollah Ali Khamenei, right, meets with Japanese Prime Minister Shinzo Abe, center, as Iranian President Hassan Rouhani sits at left, in Tehran, Iran, Thursday, June 13, 2019. A portrait of the late Iranian revolutionary founder Ayatollah Khomeini hangs on the wall. (Office of the Iranian Supreme Leader via AP)
In this picture released by the official website of the office of the Iranian supreme leader, Supreme Leader Ayatollah Ali Khamenei, right, meets with Japanese Prime Minister Shinzo Abe, center, as Iranian President Hassan Rouhani sits at left, in Tehran, Iran, Thursday, June 13, 2019. A portrait of the late Iranian revolutionary founder Ayatollah Khomeini hangs on the wall. (Office of the Iranian Supreme Leader via AP)
This undated photograph from the United Arab Emirates' Mission to the United Nations released Thursday, June 6, 2019, shows debris from the Saudi-owned oil tanker Amjad off the coast of Fujairah, United Arab Emirates. A joint statement released Thursday by Saudi Arabia, the UAE and Norway said the damage done to the four oil tankers off the UAE likely came from limpet mines placed by a
This undated photograph from the United Arab Emirates’ Mission to the United Nations released Thursday, June 6, 2019, shows debris from the Saudi-owned oil tanker Amjad off the coast of Fujairah, United Arab Emirates. (United Arab Emirates’ Mission to the United Nations via AP)
This photograph released by the state-run Saudi Press Agency shows damage inside Abha Regional Airport after an attack by Yemen's Houthi rebels in Abha, Saudi Arabia, Wednesday, June 12, 2019. Yemen's Iranian-backed Houthi rebels said they attacked the airport with a cruise missile. Saudi officials said the attack wounded more than 20 people. (Saudi Press Agency via AP)
This photograph released by the state-run Saudi Press Agency shows damage inside Abha Regional Airport after an attack by Yemen’s Houthi rebels in Abha, Saudi Arabia, Wednesday, June 12, 2019. Yemen’s Iranian-backed Houthi rebels said they attacked the airport with a cruise missile. Saudi officials said the attack wounded more than 20 people. (Saudi Press Agency via AP)
This photograph released by the state-run Saudi Press Agency shows debris on the tarmac of Abha Regional Airport after an attack by Yemen's Houthi rebels in Abha, Saudi Arabia, Wednesday, June 12, 2019. Yemen's Iranian-backed Houthi rebels said they attacked the airport with a cruise missile. Saudi officials said the attack wounded more than 20 people. (Saudi Press Agency via AP)
This photograph released by the state-run Saudi Press Agency shows debris on the tarmac of Abha Regional Airport after an attack by Yemen’s Houthi rebels in Abha, Saudi Arabia, Wednesday, June 12, 2019. Yemen’s Iranian-backed Houthi rebels said they attacked the airport with a cruise missile. Saudi officials said the attack wounded more than 20 people. (Saudi Press Agency via AP)
Japanese Prime Minister Shinzo Abe speaks with media during a joint press conference with Iranian President Hassan Rouhani, after their meeting at the Saadabad Palace in Tehran, Iran, Wednesday, June 12, 2019. The Japanese leader is in Tehran on an mission to calm tensions between the U.S. and Iran. (AP Photo/Ebrahim Noroozi)
Japanese Prime Minister Shinzo Abe speaks with media during a joint press conference with Iranian President Hassan Rouhani, after their meeting at the Saadabad Palace in Tehran, Iran, Wednesday, June 12, 2019. The Japanese leader is in Tehran on an mission to calm tensions between the U.S. and Iran. (AP Photo/Ebrahim Noroozi)
FILE - This May 13, 2019, file photo provided by the United Arab Emirates' National Media Council shows the Norwegian-flagged oil tanker MT Andrea Victory off the coast of Fujairah, United Arab Emirates. International investigators believe last month's attacks on oil tankers in a United Arab Emirates port were led by a foreign state using divers on speed boats who planted mines on the vessels. (United Arab Emirates National Media Council via AP, File)
FILE – This May 13, 2019, file photo provided by the United Arab Emirates’ National Media Council shows the Norwegian-flagged oil tanker MT Andrea Victory off the coast of Fujairah, United Arab Emirates. International investigators believe last month’s attacks on oil tankers in a United Arab Emirates port were led by a foreign state using divers on speed boats who planted mines on the vessels. (United Arab Emirates National Media Council via AP, File)
Japanese Prime Minister Shinzo Abe, left, and Iranian President Hassan Rouhani, attend a joint press conference after their meeting at the Saadabad Palace in Tehran, Iran, Wednesday, June 12, 2019. The Japanese leader is in Tehran on an mission to calm tensions between the U.S. and Iran. (AP Photo/Ebrahim Noroozi)
Japanese Prime Minister Shinzo Abe, left, and Iranian President Hassan Rouhani, attend a joint press conference after their meeting at the Saadabad Palace in Tehran, Iran, Wednesday, June 12, 2019. The Japanese leader is in Tehran on an mission to calm tensions between the U.S. and Iran. (AP Photo/Ebrahim Noroozi)
In this picture released by an official website of the office of the Iranian supreme leader, Japanese delegates attend a meeting with Supreme Leader Ayatollah Ali Khamenei, in Tehran, Iran, Thursday, June 13, 2019. (Office of the Iranian Supreme Leader via AP)
In this picture released by an official website of the office of the Iranian supreme leader, Japanese delegates attend a meeting with Supreme Leader Ayatollah Ali Khamenei, in Tehran, Iran, Thursday, June 13, 2019. (Office of the Iranian Supreme Leader via AP)
Iranian President Hassan Rouhani listens during a joint press conference with Japanese Prime Minister Shinzo Abe, after their meeting at the Saadabad Palace in Tehran, Iran, Wednesday, June 12, 2019. The Japanese leader is in Tehran on an mission to calm tensions between the U.S. and Iran. (AP Photo/Ebrahim Noroozi)
Iranian President Hassan Rouhani listens during a joint press conference with Japanese Prime Minister Shinzo Abe, after their meeting at the Saadabad Palace in Tehran, Iran, Wednesday, June 12, 2019. The Japanese leader is in Tehran on an mission to calm tensions between the U.S. and Iran. (AP Photo/Ebrahim Noroozi)
Japanese Prime Minister Shinzo Abe, center, reviews an honor guard as he is welcomed by Iranian President Hassan Rouhani, left, in an official arrival ceremony at the Saadabad Palace in Tehran, Iran, Wednesday, June 12, 2019. The Japanese leader is in Tehran on an mission to calm tensions between the U.S. and Iran. (AP Photo/Ebrahim Noroozi)
Japanese Prime Minister Shinzo Abe, center, reviews an honor guard as he is welcomed by Iranian President Hassan Rouhani, left, in an official arrival ceremony at the Saadabad Palace in Tehran, Iran, Wednesday, June 12, 2019. The Japanese leader is in Tehran on an mission to calm tensions between the U.S. and Iran. (AP Photo/Ebrahim Noroozi)
Two oil tankers near the Strait of Hormuz were damaged in suspected attacks on Thursday, an assault that left one ablaze and adrift as sailors were evacuated from both vessels and the US Navy rushed to assist. (June 13)
Two oil tankers near the Strait of Hormuz were damaged in suspected attacks on Thursday, an assault that left one ablaze and adrift as sailors were evacuated from both vessels and the US Navy rushed to assist. (June 13)