Russian intelligence operatives using energy weapons may have been behind Havana Syndrome, according to a new investigation into the mysterious and debilitating condition that struck U.S. personnel in Cuba.

“Unexplained anomalous health incidents, also known as Havana Syndrome, may have their origin in the use of directed energy weapons” used by Russia’s foreign military intelligence agency, the GRU, according to a joint investigation published by independent Russian outlet The Insider, CBS‘ 60 Minutes and German news website Der Spiegel.

The new report pinpointed one unit, referred to as the 29155, as responsible.

The U.S. Embassy in Havana on October 3, 2017. Russian intelligence operatives may have been behind Havana Syndrome, according to a new investigation into the mysterious and debilitating condition that struck U.S. personnel in Cuba…

The U.S. Embassy in Havana on October 3, 2017. Russian intelligence operatives may have been behind Havana Syndrome, according to a new investigation into the mysterious and debilitating condition that struck U.S. personnel in Cuba from 2016. YAMIL LAGE/AFP via Getty Images

Unusual symptoms were first identified by U.S. officials at the embassy in Havana in 2016.Those affected by the condition reported a range of symptoms, including memory loss, problems with hearing, insomnia and what appeared to be evidence of brain injury. More than 1,000 people in the U.S. and elsewhere are thought to be affected by Havana Syndrome, which U.S. intelligence officially terms “anomalous health incidents.”

According to the new joint investigation, the first of the “attacks” may have been recorded in Frankfurt, Germany, in 2014.

The three outlets “uncovered documentary evidence that Unit 29155 has been experimenting with exactly the kind of weaponized technology experts suggest is a plausible cause for the mysterious medical condition” referred to as Havana Syndrome, the investigation added.

Senior members of Unit 29155 were praised and rewarded for efforts related to “non-lethal acoustic weapons,” The Insider wrote. Unit 29155 operatives “have been geolocated to places around the world just before or at the time of reported anomalous health incidents,” the outlet added.

Speculation has long focused on some form of energy or acoustic weapon as possibly responsible for the symptoms displayed by U.S. officials in Cuba and elsewhere.

David Relman, a professor of medicine at Stanford University, told CBS News in February 2022 that research into the symptoms appeared to show “clear evidence of an injury to the auditory and vestibular system of the brain.”

A study published by the National Institutes of Health in March offered no further insight into the causes of the condition.

In March 2023, a U.S. intelligence investigation concluded that it was “very unlikely” that a foreign adversary was behind the symptoms.

“There is no credible evidence that a foreign adversary has a weapon or collection device” causing the symptoms, the report added. U.S officials said the lack of explanation did not discredit the symptoms described by U.S. personnel and their family members.

Update 4/1/2024 at 4:40 a.m. ET: This article was updated with additional information.