A U.S. government report released Saturday points to radiofrequency energy as the likely source of the mysterious illness that made many U.S. diplomats, as well as other countries’ diplomats, serving in Havana, Cuba sick back in 2017. Additionally, the report cites strong evidence implying that the illness was likely caused by attacks. Radiofrequency energy, it should be noted, is a type of radiation that includes microwaves.

While the reports of these symptoms arose in August 2017, the reports themselves date back to late 2016.

More than 40 U.S. government employees were affected by this illness between 2016 and 2018, according to Reuters.

Researchers from the National Academies of Sciences, Engineering, and Medicine concluded that the symptoms experienced by those diplomats in Havana—such as dizziness, nausea, visual impairments, hearing a loud sound, and headaches—were “consistent with a directed radio frequency (RF) energy attack”. This illness has come to be known as Havana syndrome.

Furthermore, the 19-person committee stated that “directed, pulsed radiofrequency energy” was “the most plausible mechanism” in explaining Havana syndrome but that secondary factors and other possible causes also bringing about these symptoms could not be taken off the table.

Other U.S. government employees stationed in Cuba and other places have also reported similar symptoms, such as in China and Russia. In June 2018, the U.S. State Department announced that it had withdrawn diplomats from China over worries that they were experiencing such symptoms.

The 2017 illnesses in Havana sparked rumors and speculation that it was a deliberate attack carried out by a foreign country hostile to the United States, with many U.S. officials suspecting Russia.

While the report doesn’t name any country or entity as the origin of these likely attacks, the researchers cited Western, Russian, and Soviet studies on pulsed radiofrequency technology and the exposure of military personnel stationed in “Eurasian communist countries” to this radiation who reported similar symptoms, saying these “provide circumstantial support for this possible mechanism.”

Both Russia and Cuba have denied any involvement in the likely attacks, according to NBC News.

Back in October, U.S. Secretary of State Mike Pompeo said “We’ve done a lot of work to try and identify how this all took place,” when asked about the investigation at a press conference. “And we continue to try and determine precisely the causation of this while doing our best to make sure we’re taking care of the health and safety of these people.”

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