"Could be, but I honestly cannot - I don't want to suggest until we can draw some more definitive conclusions who it might be. But there are a number of possibilities," Burns said in the interview published on Thursday when asked if Russia is behind the Havana syndrome.
For years, similar accusations against Russia about these types of attacks have emerged in American media outlets from time to time, with Moscow repeatedly denying them. In 2017, the Russian Foreign Ministry characterized the US allegations as completely absurd and strange.
Williams said he believes the Havana syndrome is real and serious and the CIA is determined to find out what or who is causing it. The CIA director said there have been a couple of hundred incidents of people experiencing the Havana syndrome across the US government and across the world.