The chief of the FBI's cyber engagement and intelligence section, David Ring, alleged that Russia is a "permissive operating environment" for cyber criminals and it "is not going to get any smaller" during the confrontation between Russia and the West over Ukraine, the broadcaster reported.

Ring added that the United States may face "a possible increase in cyber threat activity" from state-backed Russian hackers.

The FBI chief requested officials and business leaders increase their cyber security preparedness, considering the possibility of ransomware attacks disrupting the delivery of critical services.

Russia has repeatedly denied accusations it is involved in malicious cyber activity against the US or its European partners.