Map locating where oil tankers explode in Gulf of Oman.

MANAMA, Bahrain — The United States blamed Iran for attacks on two oil tankers in the Gulf of Oman on Thursday, as the escalating tensions in the region sparked concerns about the potential for a wider conflict.

“Taken as a whole, these unprovoked attacks present a clear threat to international peace and security, a blatant assault on the freedom of navigation and an unacceptable campaign of escalating tension by Iran,” U.S. Secretary of State Mike Pompeo said at a Washington news conference.

Pompeo said the assessment was based on intelligence, the types of weapons used and the sophisticated nature of the attacks, framing the incident as part of a wider series of assaults by Iran and its “surrogates” in the region.

Pompeo did not offer evidence during his announcement and did not take questions from reporters.

Crews had to be rescued at sea after the incidents near the Strait of Hormuz, a key shipping route for oil between Iran and the Arabian Peninsula. Global oil prices surged after the alleged attacks.

The Norwegian company Frontline said a fire broke out on its Front Altair oil tanker after an explosion. Kokuka Sangyo, the Japanese company operating the Kokuka Courageous, said their tanker had been attacked.

The 21-member Filipino crew on the Kokuka Courageous abandoned the ship and were later were rescued from a lifeboat. Its methanol cargo was intact, and the freighter was not in danger of sinking, said a spokesman for Bernhard Schulte Shipmanagement, the German shipping company that managed the ship.

Despite damage, there were no immediate concerns for the environment.

Last month, the U.S. blamed Iran for attacks targeting four tankers in the Gulf of Oman, though it has not offered proof. Iran denied the accusations.

A week later, Iran-linked Houthi rebels in Yemen claimed responsibility for drone attacks on two oil pipeline booster stations operated by Iran’s regional rival Saudi Arabia in Riyadh province.

The U.S. then announced military movements to the Gulf region, raising the prospect of a further escalation between Washington and its Sunni Arab allies, on the one side, and Iran on the other.

Iran is investigating the cause and has sent several teams of experts to fly over the scene, according to a spokesman for the Maritime Search and Rescue Centre in the southern Iranian province of Hormozgan.

Iranian Foreign Minister Mohammad Javad Zarif said the incident involving the tanker connected to Japan was suspicious, as it coincided with a high-profile meeting between Japanese Prime Minister Shinzo Abe and Iran’s Ayatollah Ali Khamenei in Tehran.

President Donald Trump referred to the visit and thanked Abe, but said it is “too soon” to make a deal with Iran, saying both sides were not yet ready. Previously, the president had indicated he might be willing to talk with Iran.

The U.S. pulled out of the 2015 nuclear deal with Iran last year and has since imposed a raft of tough sanctions on Tehran. Beyond the nuclear issue, the U.S. has turned its focus to Iran’s support for Shiite militias in the Middle East.

U.N. Secretary-General Antonio Guterres expressed concern after the latest incidents and warned of a potential “major confrontation” in the Gulf region, saying that is something the world cannot afford.

“I note with deep concern this morning’s security incident in the Strait of Hormuz. I strongly condemn any attack against civilian vessels,” Guterres said in remarks to the U.N. Security Council in New York.

The council is expected to hold a closed-door discussion on the attacks Thursday at the request of the United States.

Iranian media released footage said to be of the fire on the Front Altair, which its operator said was loaded with 75,000 tonnes of the flammable oil naphtha. Iranian authorities have referred to “explosions” and not “attacks.”

A spokesman for Frontline, the owner of the Front Altair, said there was an explosion and a fire. “We are not confirming an attack because we can’t,” the spokesman told dpa. The company said “there has been no marine pollution reported.”

The U.S. Navy in Bahrain was providing assistance after receiving two separate distress calls early Thursday, U.S. military spokesman Joshua Frey said.