A Central Intelligence Agency (CIA) official traveling with India Director of Service William Burns this month reported symptoms compatible with Havana Syndrome, CNN and the New York Times reported on Tuesday.
The unnamed officer needed medical attention, CNN reported, citing unnamed sources.
About 200 U.S. officials and their families have developed Havana Syndrome, a mysterious series of symptoms that includes migraines, nausea, memory lapses and dizziness. This syndrome was first reported by officials at the US Embassy in Cuba in 2016.
A CIA spokesman told Reuters that the agency had not commented on specific incidents or officers. "We have protocols that apply when individuals report possible abnormalities of health, which include receiving appropriate medical treatment," the spokesman said.
Last month, US Vice President Kamala Harris delayed her arrival in Hanoi for three hours when the US embassy there announced that someone had reported a health incident compatible with Havana Syndrome.
Burns said in July that he had commissioned a high-ranking official who had previously led the manhunt for Osama bin Laden to lead a strike team investigating the syndrome.
A committee of the US National Academy of Sciences has found that the most plausible theory is that "directed, pulsed radio frequency energy" causes this syndrome.
Burns has said that there is a "very high probability" that this syndrome will be deliberately caused and that Russia could be responsible.