First experienced by CIA agents on a mission in Cuba in 2016, the symptoms are described as uncomfortable sound. Some people said it was a high pitched buzzing sound, while others described it as the sound of grinding metal. One person even likened it to standing in an invisible beam of energy – and the experience was said to last for several minutes. Washington has reported incidents of the strange illness in every single continent, with a spike in cases over the last few months including in Berlin, Vienna and Vietnam.

       There are suspicions that it could be a deliberate attack by the Kremlin on US officials.

       Marc Polymeropoulos, a former CIA officer, told BBC Radio 4’s Today Programme: “This is an act of war against U.S officials.

       “We have to find out who’s doing this.”

       He believes he came down with the illness in Moscow back in 2017 and said that finding an answer to the origins of this virus is a matter of urgency.

       The CIA has now set up a task force that is being led by the same man responsible for the hunt for Al Qaeda terrorist Osama Bin Laden.

       While some experts have suggested that the illness is purely a psychological condition that is brought about from stress, others believe it to be a deliberate attack.

       Bill Evanina, a former senior US intelligence official, said; “Was it an offensive weapon in some manner or form targeted to individuals? I believe it was.

       “You may ask yourself if the Russian government was increasing and propagating their intelligence operation in Cuba, probably not good for them to have the US in Cuba in mass to identify some of things that have happened there”

       A major US study in December suggested that pulse high energy microwaves may be responsible for at least some of the cases.

       Professor David Relman, who chaired the study, said: “For many of these people, real neurological injury took place.

       READ: Joe Biden could launch ARMED operation against Cuba

       "It took place through a mechanism that we cannot precisely pinpoint, but we think could be linked to pulse microwave energy."

       Cases this year have "provided new evidence" on the theory that Russia is behind some kind of microwave attack, as tests showed "blood markers indicating some kind of brain injury".

       Experts were able to confirm a diplomat was suffering injuries by responding quickly to reports of the symptoms.

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       The Russian ministry has dismissed the claims that they have microwave weapons.

       In 2015, ？diplomatic relations between the US and Cuba ？were restored after decades of tension.

       But within two years,？Havana syndrome almost shut the embassy down, as staff were removed because of concerns for their safety.

       Initial speculation pointed to the Cuban government as being responsible, but others have pointed to Russia.

       What makes this even more odd is that records show that those who have suffered from the virus are disproportionately intelligence officers.