The US government is reported to have issued a new warning over "very real" Havana Syndrome, urging diplomats and intelligence officers to immediately flee the area if they begin experiencing symptoms.
The White House sent a memo to the Pentagon last week that "anomalous health incidents" - also known as "Havana Syndrome" because it was first detected in Cuba - pose a real and serious danger.
Those experiencing a sudden and acute onset of pressure, sound or heat in the head should report them as soon as possible.
Havana Syndrome emerged in Cuba in 2016 when two-dozen CIA officers reported suffering from a "buzzing" and intense pressure in their skull, nausea and dizziness.
A study of affected diplomats found they had experienced some form of brain injury, but could not determine the cause. There is no expert consensus on the syndrome's cause, but a co-author of the study considered microwave weapons "a main suspect". Others believe it may be the result of sonic boom attacks.