At least two more U.S. officials at the American embassy in Berlin, Germany, have sought treatment in recent weeks for symptoms of the mysterious "Havana syndrome," according to a report.

The individuals have been experiencing nausea, severe headaches, ear pain, fatigue, insomnia and sluggishness – symptoms that have sometimes left them unable to work, The Wall Street Journal first reported, citing unidentified diplomats familiar with the matter.

The newspaper said these cases represent the first to be reported in a NATO country hosting U.S. troops and nuclear weapons. U.S. officials stationed in other European nations that are not NATO participants have reported symptoms affiliated with Havana syndrome in the past.

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Those affected have included intelligence officers or diplomats working on Russia-related issues such as gas exports, cybersecurity and political interference, the Journal reported. In July, NBC News reported the first case of Havana syndrome detected at the American embassy in Berlin.

National Intelligence Director Avril Haines and CIA Director Bill Burns have been investigating a growing number of reported injuries and illnesses possibly linked to directed energy attacks in what's known as the syndrome. Still, no definitive cause or culprits have been determined.

In July, the CIA appointed a new director of its task force investigating syndrome cases, an undercover official who participated in the hunt for Usama bin Laden. The State Department also announced in July that additional cases were under investigation at the U.S. embassy in Vienna, Austria.

The task force was first formed in December after a panel of scientists from the National Academies of Sciences, Engineering, and Medicine identified "directed, pulsed radio frequency (RF) energy" as the most likely cause of the Havana syndrome – which received its name because symptoms were first reported by diplomats at the U.S. embassy in Cuba’s capital city in 2016.

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The latest cases come as intelligence agencies are having to adapt to the military withdrawal from Afghanistan, as well as their reviews into COVID-19 origins. 

The Associated Press contributed to this report.