WASHINGTON, United States (AFP) — Russian intelligence has been linked to mysterious so-called Havana Syndrome symptoms experienced by American diplomats, a media investigation said Monday, but the State Department stood by its assessment that no foreign actor was responsible.

Havana Syndrome was first publicly reported in 2016 when US diplomats in Cuba’s capital reported falling ill and hearing piercing sounds at night, sparking speculation of an attack by a foreign entity using an unspecified sonar weapon.

Other symptoms including bloody noses, headaches and vision problems were later reported by embassy staff in China, Europe and the US capital Washington.

The diplomats may have been targeted by Russian sonic weaponry, according to the joint report by The Insider, Der Spiegel and CBS’s “60 Minutes” news program.

The year-long investigation “uncovered evidence suggesting that unexplained anomalous health incidents, also known as Havana Syndrome, may have their origin in the use of directed energy weapons wielded by members of (the Russian GRU) Unit 29155,” the report said.

Russia’s Unit 29155 is responsible for foreign operations and has been blamed for several international incidents, including the attempted poisoning of defector Sergei Skripal in Britain in 2018.

The US in 2017 withdrew non-essential employees from its recently reopened embassy in Havana and expelled Cuban diplomats over the illnesses, speculating that microwave or other electronic warfare was responsible.

But US intelligence later concluded that the symptoms were more likely the result of preexisting conditions, conventional illnesses and environmental factors.

State Department spokesperson Matthew Miller, asked about the new report, said there had been no change in that assessment.

“It has been the broad conclusion of the intelligence community since March 2023 that it is unlikely a foreign adversary is responsible for these anomalous health incidents,” Miller told reporters.

Moscow dismissed the new allegations as “groundless.”

“This topic has been talked up in the press for many years already. And from the very beginning, most often it’s linked to the Russian side,” Kremlin spokesperson Dmitry Peskov told a news conference.

“But nobody has ever published any convincing evidence, so all this is nothing more than a groundless and unfounded accusation,” he said.