WASHINGTON — A mysterious illness that has affected US diplomats in recent years has been linked to a Russian intelligence unit.

Personnel stationed around the globe with "Havana Syndrome" have reported unexplained symptoms such as dizziness.

They may have been targeted by Russian sonic weaponry, according to a joint investigation by The Insider, Der Spiegel and CBS's 60 Minutes.

Moscow has denied the accusations. US officials previously said it was unlikely a foreign power was to blame.

But in their assessment of "anomalous health incidents" - delivered last year - they did not give any alternative explanation, frustrating those who have been affected.

They also acknowledged there were varying levels of confidence in the assessment between the different intelligence agencies involved.

The phenomenon gets its name from Cuba's capital Havana - where the first case was detected in 2016 - though the new report suggests the first cases may have happened in Germany two years earlier.

American personnel struck with the condition - including White House, CIA and FBI staff - have complained of dizziness, headaches, difficulty concentrating and an intense and painful sound in their ears.

More than 1,000 reports of the mysterious ailment have been made, with dozens of cases still officially considered unexplained.

US lawmakers have passed legislation aimed at supporting victims - and people with confirmed brain injuries from the disease are eligible for payments.

There has long been a suspicion that those affected have been hit by directed energy or microwaves fired from hidden devices - a possibility that was acknowledged in an earlier US intelligence report.

The fresh media investigation alleges that operatives from a Russian military intelligence unit - known as 29155 - may have targeted the brains of US diplomats with "directed energy" weapons.

It says there is evidence that places members of the unit in cities around the world at times when US personnel reported incidents.

As part of the investigation, The Insider - a Russia-focused site - also reported that officers in the 29155 unit had been rewarded for their work related to the development of "non-lethal acoustic weapons."

An American military investigator examining instances of the syndrome told 60 Minutes that the common link between victims of the syndrome was a "Russia nexus".

Greg Edgreen explained: "There was some angle where they had worked against Russia, focused on Russia, and done extremely well."

He also said the official US bar of proof to show Russian involvement had been set too high, as his country did not want to "face some very hard truths".

Kremlin spokesman Dmitry Peskov denied that there was any evidence of Russian involvement and said the accusations in the report were unfounded.

One victim of the syndrome - an FBI agent - told 60 Minutes about her experience of being hit by a powerful force at her home in Florida 2021.

"Bam, inside my right ear, it was like a dentist drilling on steroids," she told the programme. "That feeling when it gets too close to your eardrum? It's like that, times 10."

The woman - known as Carrie - said she ultimately passed out, and later had issues with memory and concentration.

Responding to the report, US officials told CBS News, the BBC's US partner, that they would "continue to closely examine anomalous health incidents", but repeated their position that it was "very unlikely a foreign adversary is responsible".

But they said they did "not call into question the very real experiences and symptoms that our colleagues and their family members have reported", saying their work on such incidents was a priority. — BBC