A trip to Vietnam by US Vice President Kamala Harris was delayed on Tuesday following an unexplained health incident in Hanoi, the US Embassy in the Southeast Asian country’s capital said in a statement.

Harris, who was in Singapore concluding a three-day trip, was due to fly to Hanoi late on Tuesday but was unexpectedly delayed for three hours due to an “anomalous health incident.”

“Anomalous health incident” is a term the US government often uses to describe Havana Syndrome, a condition with symptoms such as dizziness, nausea, migraines and memory lapses, so named because it first was reported by US officials based in the US embassy in Cuba in 2016.

“The Vice President’s office was made aware of a report of a recent possible anomalous health incident in Hanoi, Vietnam,” the US Embassy statement said.

“After careful assessment, the decision was made to continue with the Vice President’s trip,” the statement said, without elaborating.

A spokesperson for Harris declined to comment on the reason for the delay.

About 100 CIA officers and family members are among some 200 US officials and kin sickened by “Havana syndrome,” CIA Director William Burns has said.

A US National Academy of Sciences panel in December found that a plausible theory is that “directed energy” beams caused the syndrome, he said.

There is a “very strong possibility” that the syndrome is intentionally caused, and that Russia could be responsible, he said, adding that he is withholding definitive conclusions pending further investigation.

Moscow denies involvement.