According to Sina Finance, U.S. officials are investigating whether Iran was behind cyberattacks on two energy tankers bound for U.S. ports in Texas.

The ships were attacked in the Strait of Gibraltar in early August while heading toward U.S. ports. One was a crude oil tanker and the other was a liquefied petroleum gas carrier.

Officials said a special team led by the U.S. Coast Guard, with FBI agents involved, boarded the two vessels after they entered the Gulf of Mexico in August. Coast Guard Cyber Command commander Rear Admiral Amy Grable declined to discuss the specific ships but said the Coast Guard cyber response team spent three to four days aboard carrying out incident response work.

According to Sina Finance, the ship tracking data and a U.S. official said one of the tankers, VL Prosperity, was carrying more than 2 million barrels of crude oil from Egypt to Galveston, Texas, when it was targeted in the Strait of Gibraltar. The vessel’s manager confirmed that U.S. authorities boarded it for a cybersecurity inspection and that it has since been cleared to resume normal operations.

The manager of the other tanker, Kohaku, did not respond to a request for comment.