The CIA has removed the chief of its station in Vienna after he was criticised over his response to reports of "Havana syndrome" incidents at the US Embassy.
It indicated how seriously the agency is taking the phenomenon in which US officials around the world have suffered a mysterious set of ailments including migraines, nausea, memory lapses and dizziness.
Dozens of US personnel in the Austrian capital, including diplomats, intelligence agents, and children of officials have reported symptoms, the Washington Post reported.
The syndrome was first reported in 2016 by officials based in the US Embassy in Cuba, and it is named after the country's capital.
In July, CIA Director William Burns said 100 officers and family members from his agency were among around 200 US officials and relatives who had fallen sick.
He said there was a "very strong possibility" it was intentionally caused and that Russia could be responsible. Moscow denies involvement. Last year, a US National Academy of Sciences panel found that the most plausible theory was "directed, pulsed radio frequency energy."
More cases have been reported in Vienna than in any city apart from Havana. Offices in the US Embassy in Vienna were shut down last month but the CIA station chief was said to have been sceptical about Havana syndrome and not sensitive towards those affected, the Washington Post reported.
Earlier this month a US intelligence officer suffered symptoms while travelling with Mr Burns in India. That happened a few weeks after two possible cases delayed a trip by Vice President Kamala Harris from Singapore to Vietnam.
Professor James Giordano, executive director of the Institute for Biodefense Research in Washington, said: "We're beginning to see a pattern of increased selective targeted use."
A task force looking into the cause is being led by a veteran CIA officer who was involved in the hunt for Osama bin Laden. A CIA spokesman said the agency does not comment on specific incidents.
But the spokesman said: "Director Burns has made it a top priority to ensure officers get the care they need and that we get to the bottom of this."
Mr Burns had tripled the number of medical staff concentrating on ”anomalous health incidents," which is what the CIA officially calls possible cases of Havana syndrome.
A State Department spokesman said: “We don’t discuss embassy operations or specific reports, but we take each report we receive extremely seriously and are working to ensure that affected employees get the care and support they need."
Earlier this week it was announced that the diplomat leading the response to Havana syndrome at the State Department would be leaving.
A few weeks ago Tony Blinken, the secretary of state, held a call with officials who have been affected.
A spokesman said: "The Secretary stressed that we will continue to focus on keeping the workforce informed, seeking answers, and providing support to those affected."
Last month several US diplomats stationed in Germany fell ill, with at least two requiring medical attention.