The United States said that Iran was behind Thursday's attacks on two oil tankers near the Strait of Hormuz.

"It is the assessment of the US government that Iran is responsible for today's attacks in the Gulf of Oman," Secretary of State Mike Pompeo told reporters. "These attacks are a threat to international peace and security, a blatant assault on the freedom of navigation, and an unacceptable escalation of tension by Iran."

Washington's top diplomat blamed Tehran hours after the tankers - one Japanese, the other Norwegian - came under attack roughly 30 nautical miles from the coast of Iran as they were exiting the Strait of Hormuz into the Gulf of Oman.

"This assessment 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," Pompeo said.

The secretary did not cite any specific evidence for the claim.

The crew members of the tankers were rescued and the US Navy's 5th Fleet said it was assisting the stricken vessels.

The strait is an important transit route for crude oil and a flashpoint in rising tensions between the US and Iran.

"We are aware of the reported attack on shipping vessels in the Gulf Oman," the Bahrain-based 5th Fleet said in a statement. "US Naval Forces in the region received two separate distress calls at 6:12 am local time and a second one at 7:00 am," it said. "US Navy ships are in the area and are rendering assistance," the statement added.

The Iranian rescue ship Naji 10 picked up 44 crew members from the tankers, 23 from one and 21 from the other, and took them to Bandar-e-Jask in the southern province of Hormozgan, the official IRNA news agency reported, later clarifying that other passing ships had also taken part in the rescue.

"Reported attacks on Japan-related tankers occurred while Prime Minister Shinzo Abe was meeting with Ayatollah Khamenei for extensive and friendly talks," Javad Zarif, Iran's foreign minister, said. "Suspicious doesn't begin to describe what likely transpired this morning."

The United Kingdom Marine Trade Operations (UKMTO) said it was investigating the alleged attack on the two tankers, the Kokuka Courageous and Front Altair.

The weapons used in the attacks in the Gulf of Oman, where four tankers were damaged last month in attacks the US attributed to Iran, appeared to have been sophisticated.

Thursday's attacks took place within around 45 minutes of each other, officials said.

Images showed that damage to one of the tankers was widespread, including a fire and a hole on the water line that appeared to be consistent with a strike by a torpedo or other water-level weapon.

Both ships caught on fire, and their crews abandoned ship although neither appeared to be in danger of sinking, authorities said.

Bernhard Schulte Ship Management, which operates Kokuka Courageous, a chemical and oil tanker, said it launched an emergency response following a security incident.

The vessel was stopped around 70 nautical miles from Fujairah in the United Arab Emirates and 14 nautical miles of the coast of Iran, according to the UKMTO.

"The 21 crew of the vessel abandoned ship after the incident on board which resulted in damage to the ship's hull starboard side," the shipping company said in a statement on its website.

"The master and crew abandoned ship and were quickly rescued from a lifeboat by the vessel Coastal Ace, a nearby vessel. One crew man from the Kokuka Courageous was slightly injured in the incident and is receiving first aid on board the Coastal Ace," the statement added.

Bernhard Schulte said the vessel was not at risk of sinking and its cargo of methanol was intact.

The director of safety policy at Japan's transport ministry, Norio Ishihara, said he had also received reports the Kokuka Courageous was carrying methanol but could not confirm the ship's cargo.

According to MarineTraffic, a ship-tracking website, the Kokuka Courageous was traveling from Al Jubail in Saudi Arabia to Singapore while Front Altair, operated by Norwegian firm Frontline, was traveling from Ruwais in the UAE, to Kaohsiung, Taiwan.

A spokesperson for Frontline told Norwegian media outlet VG that the Front Altair had caught fire.

Japanese Minister of Economy, Trade and Industry Hiroshige Seko said that his country was investigating a possible attack on tankers in the Middle East.

"We received information that two tankers which were loaded with cargo for Japan were attacked near the Strait of Hormuz. The ministry convened an emergency meeting," Seko said. The Strait of Hormuz connects the Gulf of Oman to the Persian Gulf.

Shinzo Abe, Japan's prime minister, met with senior Iranian officials in Tehran on Wednesday in a visit that aimed to de-escalate soaring tensions between the US and Iran.

The attacks on Thursday came almost exactly one month after four commercial ships were purportedly sabotaged by mines off the port of Fujairah. The US pointed the finger at Iran or Iranian "proxies."

The Gulf of Oman is connected to the Persian Gulf by the Strait of Hormuz, which has become the geopolitical focal point in rising tensions between the US and Iran since President Donald Trump's administration withdrew from the 2015 nuclear deal with Tehran and re-applied economic sanctions.

The sanctions targeted Iran's oil and banking sectors.

Brent crude rose 4 percent on Thursday to $62.37 a barrel after reports of the attacks, before slipping back to $61.30 barrel by the close of trading. EFE