The US government has paid nearly $3m in compensation to victims of so-called Havana Syndrome.
The payments are the first to be made to US agency staff in relation to the illness, which reports say began emerging a decade ago among CIA officers working in the Cuban capital.
American staff based elsewhere, including China, have reported "anomalous health incidents," and sufferers have described hearing a low hum, clicks, squeals and "grinding metal" as well as intense pressure on the skull, dizziness and nausea.
The US Department of Defence said it would continue to prioritise "the care of affected personnel" as it announced the compensation, which was paid out under the Havana Act that was signed into law in 2021.
There has been widespread speculation over what and who is responsible for Havana Syndrome, with some people claiming microwaves and prompting further conjecture that a foreign power may have used some kind of sonic or sonar weapon.
Former CIA analyst Erika Stith told CBS News in 2022, "My brain is broken," and, "We got this as a result of serving our country. And we deserve to be taken care of."
Last year, most US intelligence agencies and departments concluded it was "very unlikely" that a foreign actor used " a novel weapon or prototype device to harm " US personnel and their families, though a small component of the intelligence community did not completely dismiss the theory.
A National Intelligence Council report said none of the agencies or departments it spoke to "call[ed] into question the experiences or suffering" of US workers and their families and that the community believed they "experienced genuine, sometimes painful and traumatic, physical symptoms and sensory phenomena and honestly and sincerely reported those events as possible anomalous health incidents."
Havana Syndrome was first publicly reported in 2016, when US diplomats in Cuba reported getting sick and hearing piercing sounds at night, and other cases have been reported around the world, from Washington to China.
In 2017 the US government pulled more than half of its staff from its embassy in Havana, and Canada's government sharply reduced its personnel in Havana in 2019 after embassy employees reported similar problems.