A liquefied natural gas tanker bringing fuel from the U.S. to Europe suffered a systems failure that the crew reported as a suspected cyber attack, according to people familiar with the matter.

In the latest of a number of potential cybersecurity incidents on tankers, the Vivit Africa LNG was sailing east in the Mediterranean and Adriatic Seas toward Italy early this month when the crew were suddenly unable to access some of the internal control systems, the people said, asking not be identified because the information was not public.

Trading giant Vitol Group confirmed that it has the ship under a long-term lease known as a time charter, without commenting further.

After idling off the coast of Italy without discharging its cargo, the vessel on Wednesday began sailing away from its intended destination of Rovigo, heading back toward the Spanish port of Algeciras near the entrance to the Mediterranean, according to shipping data compiled by Bloomberg. 

The crew reported the incident early last week to Korean Register, the organization that acts as the technical and safety adviser to the South Korean-owned vessel, and investigations are ongoing, the people said. There are no indications of who the perpetrator of the suspected attack may be, they said.

Korean Register and the owner of the Vivit Africa LNG, South Korea’s H-Line Shipping Co. Ltd., didn’t immediately respond to requests for comment.

The suspected hacking of the Vivit Africa LNG follows other incidents in late August, when two oil and gas tankers off the U.S. coast were boarded by the Coast Guard and Federal Bureau of Investigation due to potential cyberattacks. American officials are monitoring nearly 20 ships around the world for such threats. 

The tanker was carrying a cargo loaded at Louisiana’s Cameron LNG terminal, ship-tracking data show. It had sailed across the Atlantic and was nearing its destination in early September, when the crew encountered the technical issues that stalled their voyage. 

The Italian Coast Guard assisted the vessel “after the master reported a malfunction in the systems used to monitor cargo parameters, requiring intervention by the company’s technicians,” Captain Roberto D’Arrigo said in an emailed statement. The cause of the problem couldn’t be identified and “the Chioggia Coast Guard intervened solely for navigation safety purposes, issuing an urgent notice to mariners to keep their distance.”

The Vivit Africa LNG used some equipment from Kongsberg Maritime, which provides positioning, navigation and propulsion technology for ships. The company is aware of reports of the incident but “it is too early to draw conclusions regarding the cause or any potential security implications,” said spokesman Jon Berge.