Secretary of State Mike Pompeo says U.S. intelligence indicates that the attacks on two tanker ships off the coast of Iran Thursday were carried out by Iran as part of large campaign of escalating tensions in region.

Pompeo said the preferred U.S. response is still sanctions and diplomacy but “the U.S. will defend our interest” in the Middle East.

The two massive tankers were attacked in the Gulf of Oman near the strategic Strait of Hormuz, an assault that left one ablaze and adrift as sailors were evacuated from both vessels.

No one has claimed responsibility or explained how the tankers were attacked.

Iran’s foreign minister called the attacks “suspicious.”

The U.S. Navy rushed to assist amid heightened tensions between Washington and Tehran.

A spokesman for the U.S. Central Command said 21 crew members rescued from the oil tanker Kokuka Courageous are now on board the Navy’s guided-missile destroyer Bainbridge following an explosion. Army Lt. Col. Earl Brown says the U.S. Navy ship was in international waters in the Gulf of Oman near the Courageous when it received a distress call at about 6 a.m. local time.

Brown says the Bainbridge provided “immediate assistance” to the Courageous and its crew members after they abandoned ship.

Also, the head of the Arab League is urging the U.N. Security Council to take action against those responsible for the recent targeting of oil tankers in the Arabian Gulf and attacks against Saudi Arabia which he called “dangerous.”

Secretary General Ahmed Aboul Gheit told a council meeting Thursday on cooperation between the U.N. and the Arab League that “some parties in our region are trying to instigate fires in our region and we must be aware of that.”

One of the tankers carried oil bound for Japan, whose Prime Minister Shinzo Abe was wrapping up a high-stakes diplomatic visit in Tehran that sought to ease tensions between Iran and the United States.

The U.S. Navy is providing support to the damaged vessels.

“U.S. Naval Forces in the region received two separate distress calls at 6:12 a.m. local time and a second one at 7:00 a.m. U.S. Navy ships are in the area and are rendering assistance,” Navy Cmdr. Josh Frey, spokesman for Bahrain-based U.S. Fifth Fleet, told Navy Times in an emailed release.

The U.S. Navy’s guided missile destroyer Bainbridge is serving as the command vessel for the U.S. response, Lt. Col. Earl Brown, a spokesman for U.S. Central Command, told Military Times.

Both vessels were outbound from the Persian Gulf on June 12 before being attacked in the Gulf of Oman, outside the straits, according to data on the commercial shipping tracking website Marine Traffic.

The reported attack occurred in sea lanes that U.S. officials say have been heavily mined by the Iranian military.

The CENTCOM spokesman said it was too early to speculate about what caused the incident or who may have been behind it. “We are just rendering aid at this point," Brown said.

He would not comment about what, if any further U.S. response would take place as a result of this incident.

Brown told Military Times that a Norwegian tug boat is also assisting.

Benchmark Brent crude spiked at one point by as much 4 percent in trading following the reported 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.

The latest incident comes after the U.S. alleged that Iran used mines to attack four oil tankers off the nearby Emirati port of Fujairah last month. Iran has denied being involved, but it comes as Iranian-backed rebels in Yemen also have launched missile and drone attacks on Saudi Arabia.

The firm that operates the Front Altair told The Associated Press that an explosion was the cause of the fire onboard. International Tanker Management declined to comment further saying they are still investigating what caused the explosion. Its crew of 23 is safe after being evacuated by the nearby Hyundai Dubai vessel, it said.

The second vessel was identified as the Kokuka Courageous. BSM Ship Management said it sustained hull damage and 21 sailors had been evacuated, with one suffering minor injuries.

The Japanese trade minister said the two tankers were carrying "Japan-related” cargo. Hiroshige Seko said on Thursday that all crew members were safely rescued. He said the government has set up a task force and that the government has informed the shipping industry to use precautions.

The Japan Shipowners' Association said one of the two ships attacked is a Panamanian-registered chemical tanker belonging to its Japanese member and was on its way to Singapore and Thailand, not to Japan.

It said all 21 Filipino crewmembers were uninjured.

The timing of Thursday's reported attack was especially sensitive as Abe's high-stakes diplomacy mission was underway in Iran. 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.

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.

Abe met with Iran's Supreme Leader Ayatollah Ali Khamenei on Thursday, the second and final day of his visit. There were no immediate details about what they discussed.

Meanwhile, in Tokyo, Japan's Chief Cabinet Secretary Yoshihide Suga, a top government spokesman, told reporters that Abe's trip was intended to help de-escalate tensions in the Mideast — but not specifically mediate between Tehran and Washington.

His remarks were apparently meant to downplay and lower expectations amid uncertain prospects for Abe's mission.

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.

Iran's nuclear deal, reached in 2015 by China, Russia, France, Germany, the United Kingdom and the U.S., saw Tehran agree to limit its enrichment of uranium in exchange for the lifting of crippling sanctions. Western powers feared Iran's atomic program could allow it to build nuclear weapons, although Iran long has insisted its program was for peaceful purposes.

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.

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Associated Press writers Aya Batrawy in Dubai, Mari Yamaguchi in Tokyo and Amir Vahdat in Tehran, Iran, and Military Times managing editor Howard Altman And Navy Times reporter Mark Faram contributed to this report.