The mysterious head injuries suffered by US diplomatic staff in China and Cuba that had been described as "sonic attacks" are consistent with the use of directed microwave energy, according to a report published Saturday by the National Academy of Sciences.
"Overall, directed pulsed RF (radio frequency) energy, especially in those with the distinct early manifestations, appears to be the most plausible mechanism in explaining these cases among those that the committee considered," the report said.
The report added that it considered possible incidents of persistent postural-perceptual dizziness as a possible secondary issue in some of those affected a contributing factor.
While the report does not conclude that the use of directed microwave energy in these instances was done deliberately, it said such action could be used for nefarious purposes.
"The mere consideration of such a scenario raises grave concerns about a world with disinhibited malevolent actors and new tools for causing harm to others, as if the U.S. government does not have its hands full already with naturally occurring threats," the report said.
The report said that it considered chemical exposures, infectious diseases and psychological issues as potential causes or aggravating factors of the injuries, but the overall analysis appeared to show they were not the likely cause.
A 19-person committee of medical and scientific experts produced the report at the request of the State Department.
CNN reported last year that doctors shared what happened to the brain of one diplomat who may have been the victim of one of the attacks.
Researchers revealed the results of an independent brain analysis of Mark Lenzi, a US diplomat who was stationed in Guangzhou, China, in 2017 when he started experiencing unexplained symptoms, including headache, difficulty reading, irritability, as well as memory and sleep problems.
Among the MRI findings: 20 brain regions with "abnormally low" volumes, including regions involved in memory, emotional regulation and motor skills that may correlate with Lenzi's symptoms, doctors said. Of the 107 regions they looked at, they also found three that had bigger volumes.
Researchers said the parts of the brain with low volume may reflect brain injury, and those with high volumes could be evidence that other parts of his brain have compensated.
Most of the documented attacks came in 2016 and 2017, though there were a handful of reported incidents after that as well.
CNN reported in 2018 that a senior administration official said investigators tore apart buildings where diplomatic employees encountered the sounds but found no acoustic devices. That lead law enforcement to believe the injuries were the result of microwaves beamed from a nearby location and that the "sounds" were merely a means of masking the microwave attacks.
That was only a theory, the official said, and there was no concrete evidence to back it. However, brain scans on the injured personnel showed changes that indicate damage, the official said.
Cuban officials have consistently denied their government had any involvement with the diplomats' health problems and have said mass hysteria is the most likely cause.
The sophistication of the attacks led US officials to suspect a third country may have been involved with the incidents, but they have not been able to reach that conclusion.
In August 2017, officials included Russia among a list of countries that have an adversarial relationship with the United States and that American investigators suspected might be involved.
Russia is one of the few countries that have used microwave technology before, and a theory among investigators was that some rogue Cuban intelligence officials worked with Russia because they were unhappy with the détente between United States and Cuba, a senior administration official said at the time.