A Central Intelligence Agency officer in the United States who had travelled to India in September with agency director William Burns reported symptoms consistent with the mysterious health ailment known as Havana syndrome, CNN reported on Monday.

The syndrome was first reported by American diplomats and other government employees in the Cuban capital Havana starting in 2016. Some of those impacted by Havana syndrome have reported migraines, nausea, memory lapses and dizziness as symptoms.

The Central Intelligence Agency officer was given immediate medical treatment when he returned to the United States, CNN reported, citing three sources.

A number of theories have been floated to explain the mysterious symptoms, including microwave weapons or sonic attacks, possibly as a part of an espionage or hacking plan. All of them are unproven though.

Burns was “fuming” with anger after the incident. Some former Central Intelligence Agency officials told The New York Times that this would be an egregious escalation if it was a targeted attack or if an adversarial power was behind the syndrome.

A spokesperson of the Central Intelligence Agency said that the agency does not comment on specific incidents or officers. “We have protocols in place for when individuals report possible anomalous health incidents that include receiving appropriate medical treatment,” the spokesperson added.

Last month, Vice President Kamala Harris delayed her visit to Vietnam by three hours after a possible case of Havana syndrome was reported in Hanoi.