BRUSSELS (AP) — At least two energy companies in the Belgian ports of Antwerp and Ghent have been hit by cyberattacks and Belgian authorities have opened an investigation, one day after Germany opened a probe into similar attack, an official said Thursday.

“An investigation by the Federal Computer Crime Unit has started,” said Kristof Aerts of the prosecutor’s office in Antwerp, Europe’s second-largest port with large fossil fuel facilities.

In Germany, Hamburg prosecutors said they opened an investigation into suspected blackmail after two companies involved in storing and supplying oil and other materials said Tuesday they had been hit by a cyberattack that impacted operations.

Aerts did not provide specific details of the companies involved in Belgium, or of links with Germany but added that cyberattacks “are naturally an international story, so that will certainly be looked at. It is especially why the expertise of the Federal Computer Crime Unit is essential.”

The damage the attack caused was unclear but there appeared to be limited immediate impact.