A number of US diplomats stationed in Germany have fallen ill with the unexplained condition known as “Havana Syndrome”, it has emerged, marking the first time the condition was detected in a Nato country.

US intelligence reportedly believes Russia may be behind the mysterious condition, which causes ear pain, sudden dizziness, severe headaches and confusion.

At least two US officials based in Germany required medical attention for the condition in recent months, according to the Wall Street Journal.

The American embassy in Berlin declined to comment on specific cases but said the US would leave no stone unturned in its efforts to protect its diplomats.

The German foreign ministry said it was aware of the reports but could not provide any further details.

“Havana Syndrome” is named after the Cuban capital, where the first cases were detected among American officials in 2016.

Since then it has affected diplomats and intelligence officers in a number of countries around the world, including Britain, where two officials accompanying former President Donald Trump on his state visit in 2019 fell ill with suspected cases of the condition. 

a gate in front of a building: The sydrome is named after the Cuban capital, where US embassy workers were first diagnosed with the syndrome - Emily Michot/Miami Herald/Tribune News Service via Getty Images

Around two dozen American diplomats and intelligence officers based in Vienna have been affected this year.

Those affected include intelligence officers or diplomats working on Russia-related issues such as gas exports, cybersecurity and political interference.

“There is no evidence about what happened to us, but it is striking that some of us had worked on Russia-related issues,” the newspaper quoted an unnamed American official who was flown home for treatment as saying.  

US intelligence is said to believe Russia may be using powerful microwave devices to steal data from the targets’ mobile phones and computers, and that the condition is an unintentional side effect.

But Germany’s Spiegel magazine on Wednesday claimed to have uncovered evidence Russia has long been working on a way to send dangerous radio waves via a target’s mobile phone.

If true, that might explain why some of those targetted appeared to suffer new attacks even after returning to the US — something that has puzzled US investigators.

The news the condition appears to have spread to diplomats based in Germany will concern the US and its allies. They are the first known cases to affect US officials permanently based in a Nato member — and one that is home to major American military bases and nuclear weapons.

It has also affected American officials based in a number of other, as yet undisclosed European countries, according to the Wall Street Journal.

The official said symptoms of the condition were preceded by piercing ear pain, high-pitched electronic noise and pressure in the ears at night or in the early hours of the morning.

An early FBI investigation concluded that the initial cases in Havana were probably a case of “mass psychogenic illness”, where a group of people start to show symptoms because they believe they are sick.

But more recent US medical investigations have found evidence of physical brain injuries in those who have been affected by the condition.

Doctors at the Walter Reed National Military Medical Center have reportedly compared the brain injuries to those caused by shockwaves from an explosion.

A scientific report commissioned by the US government last year found the injures could be caused by some form of microwave weapon.