At least two foreign tankers bound for American shores were targeted in cyberattacks now under U.S. government investigation, fueling concerns that Iran or other adversaries are seeking to widen the Middle East conflict, according to U.S. officials familiar with the incidents.

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

The inspection 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.

The tankers were transiting the Strait of Gibraltar earlier in August when they were attacked, according to ship tracking data and one of the officials. That location, as well as the destination of the ships, is likely to raise concerns that the attackers were trying to disrupt a key maritime chokepoint or attack a U.S. port.

The vessels were carrying oil and liquefied natural gas, raising the risk of a catastrophic explosion or an oil spill. Ships run on integrated systems that, if compromised, could shut down the engine or force the crew to lose control of navigation.

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

U.S. authorities haven't confirmed whether Iran or another adversary like Russia or China is behind the attacks. But officials say they are concerned the recent incidents are opening up a new front in the seven-month war. Bloomberg News earlier reported one of the boardings.

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 Wall Street 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."