Germany's BSI federal cyber agency on Monday said it was aware of additional German institutions affected by the WannaCry "ransomware" cyber attack beyond those companies already known, and it expected additional variants of the virus to surface.

BSI President Arne Schoenbohm, in a statement, urged companies hit by the virus to report attacks through normal confidential channels to the agency, and said no payments should be made to hackers under any circumstances.

"WannaCry is another urgent wakeup call to invest more in IT security," Schoenbohm said. He urged companies to install a Microsoft patch that had been available for months.

Schoenbohm met with his counterparts from Austria, Switzerland and Luxembourg in Bonn on Monday to discuss the latest ransomware attacks as well as international coordination to defend against such attacks.