A NSC member's unusual illness is being looked into as a possible case of "Havana syndrome, CNN reported.
The term refers to unexplained symptoms first noticed in the US Embassy in Cuba.
Its causes are unclear. Some have suggested they are caused by a new kind of weapon.
A a National Security Council official falling sick yards from the White House is being connected to similar instances that have affected US officials in Cuba and China, according to CNN.
The network reported that the NSC official - who was not named - fell ill in November 2020 on the Ellipse, a large lawn to the south of the White House.
CNN cited unnamed official sources for its report.
It is one of two incidents on US soil that are being looked at as potential cases of "Havana syndrome" - a mysterious set of unexplained symptoms that have suddenly struck US officials in Cuba and China since 2016.
The issue has worried the US government for years, but has usually been reported abroad. Sources told CNN that the fact that two suspected cases have taken place domestically is has worried them.
The second US incident concerned a White House staffer who was walking her dog in Virginia in 2019, when she heard a high-pitched noise in her ears that was followed by an intense headache, according to GQ.
Very little is known for sure about the phenomenon, and investigators are treating these two instances only as suspected cases.
The phenomenon was first reported by a diplomat at the US embassy in Cuba, who heard a loud, piercing sound in one ear that was followed by a loss of balance and nausea, according to a report from the National Academies of Sciences in December.
After this, three CIA officers based in the same embassy building experienced similar sensations. Other symptoms include pain in both ears, dizziness, tinnitus, vertigo, and difficulty thinking.
The National Academies of Sciences report found that 40 State Department staff in Cuba and China had experienced similar and lasting symptoms, as Axios reported.
The cause is not agreed on, but the CIA, the State Department and most recently the Pentagon have launched investigations into it, according to CNN.
Lawmakers on the Senate and House Armed Services Committees were briefed on the issue earlier in April, the network said.
There have been multiple explanations offered for the syndrome, including a form of mass psychogenic illness or even - as some researchers have noted - that the piercing sound closely matches that of a cricket.
An early explanation was that it was the impact of some sort of sonic weapon, but the National Academies of Sciences study said in December the most likely explanation was the use of high-frequency microwaves. The report also noted that Russia has conducted significant amounts of research into the technology.
President Donald Trump blasted Cuba in an address in the Rose Garden in 2017, accusing the country of "sonic attacks." Cuban officials called his accusations "science fiction" in response, Reuters reported.
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