"It is clear we are witnessing in a more or less disguised way cyberwars between states, episodes of cyberwar between states," Guterres said during one of the opening speeches at the Munich Security Conference.

"It's high time to have a serious discussion about the international legal framework in which cyberwars take place," he said.

"The fact is we haven't been able to discuss whether or not the Geneva convention applies to cyberwar and whether international humanitarian law applies to cyberwar."

The United States and Britain on Thursday blamed the Russian military for last year's devastating "NotPetya" ransomware attack, calling it a Kremlin effort to destabilise Ukraine, which spun out of control.

The attacks ended up crippling computer networks in the United States and Europe, including those of some big companies.

Washington has also blamed North Korea for the huge "WannaCry" ransomware attack last May in which more than 300,000 computers were struck in some 150 nations.

"How to respond in cases of permanent violations of cybersecurity? What are the different uses that criminal, terror organisations are making of the web?" Guterres said.

Finding a consensus on how to respond to such attacks is urgent, he said, "especially now that artificial intelligence, that is providing enormous potential for economic development, social development, for the well-being of all, is also in the opinion of many an existential threat for humankind."

"It is necessary to bring together governments, the private sector, those involved in civil society, academics, research centres, in order to be able to establish at least some basic protocols to allow the web to be an effective instrument for the good," he said.