The U.S. is investigating whether Iran is behind the cyberattacks of two energy tankers bound for American ports, said U.S. officials familiar with the probe, which has sparked concerns that Tehran is looking for novel ways to widen the war in the Middle East.

The two tankers were transiting the Strait of Gibraltar in early August when they were hit by the attacks. The ships-an oil tanker and a liquefied petroleum tanker-were making their way to ports in Texas at the time, according to ship tracking data and one of the officials.

The location of the attacks and the destination of the tankers has raised the prospect that Iran or an Iran-aligned actor could be seeking to disrupt another key maritime chokepoint or blow up a U.S. port. Ships run on integrated systems that, if compromised, could result in an explosion, a collision or an oil spill.

A specialized team led by the U.S. Coast Guard that included agents from the Federal Bureau of Investigation boarded the two tankers in August after they arrived in the Gulf of Mexico, the officials said.

The inspections of the foreign-flagged vessels "were designed to ensure integrity of the vessel's operational and information technology systems following indications that the networks of both vessels were compromised," according to Coast Guard and FBI statements. The boardings occurred on Aug. 21 and 24, the FBI said.

One tanker, the VL Prosperity, was carrying more than two million barrels of oil from Egypt to Galveston, Texas when it was targeted in the Strait of Gibraltar, according to ship tracking data from Lloyds List Intelligence and one of the officials. It was approached by a Coast Guard vessel as it neared the shores of the U.S., the ship tracking data shows.

Iran's semiofficial news outlet Mehr News reported on the incident in August. Citing crew members, it said the attackers infiltrated the VL Prosperity's engine-room systems, reduced the engine's cooling flow, increased the engine speed, and disabled the ship's fuel and engine-oil tank. It said no group had claimed responsibility for the incident. The Wall Street Journal couldn't independently confirm the report.

The second tanker, the Kohaku, was transiting the strait on its way to another Texas port to load liquefied petroleum gas, according to ship tracking data and the U.S. official. It was approached by the same U.S. Coast Guard ship that responded to the VL Prosperity, the data shows.

The owner of the VL Prosperity and the manager of the M/T Kohaku didn't immediately respond to requests for comment.

The Coast Guard and FBI declined to say how many cyberattack cases they have investigated since the war with Iran began.

A Coast Guard spokesperson said there were no reports of vessel instability or physical danger to the crews, and that the Coast Guard is actively managing communications with port operators, vessel owners and local maritime stakeholders to ensure safe port operations.

The U.S. and Iran have been locked in a battle to control the Strait of Hormuz, a strategic waterway off Iran's coast that allows for the transit of a significant portion of the world's oil supply. Iran has attacked commercial ships trying to transit without permission or first paying a toll, prompting the U.S. to retaliate.

The Iran-backed Houthis are exerting control over another critical waterway known as the Bab al-Mandeb Strait at the mouth of the Red Sea. Iran and its proxies have sought to choke off oil shipments to pressure the U.S. and its allies in the Persian Gulf.

Similar to those chokepoints, the Strait of Gibraltar is critical for global energy markets. Each day, roughly 300 ships transit the waterway, which connects the Mediterranean Sea with the Atlantic Ocean.

Experts have warned cyberattacks on ships can be extraordinarily dangerous, depending upon the sophistication and the type of vessel involved.

The Coast Guard has specialized teams trained to respond to and investigate these kinds of attacks. Earlier this year, the teams boarded several dark fleet vessels seized by the U.S. to ensure that the ships' systems weren't compromised before arriving in the U.S. or at other ports.

"For a vessel that's carrying tens of millions of gallons of crude oil, which is highly volatile, there's always a risk of fire explosion," Rear Adm. Jason Tama, head of the Coast Guard's Cyber Command, told the Journal in June. "The atmosphere in the tanks has to be very carefully managed to ensure that you're not going to get a situation where there's a fire explosion. And then there's always a risk of an oil spill."