WASHINGTON — An intelligence officer traveling in India this month with the C.I.A. director reported symptoms consistent with the so-called Havana syndrome, signaling a possible escalation in the mysterious incidents that have affected American officials since 2016, current and former officials said.
The circumstances of the incident are still being investigated, and officials have not yet determined whether the C.I.A. officer was targeted because the officer was traveling with the director, William J. Burns, or for other reasons. If the incident was caused by an adversarial intelligence service, it may not have known the officer was traveling with Mr. Burns.
Officials have struggled to determine the cause of the symptoms. While some officials are convinced they are attacks and that one or more rival powers are responsible, intelligence agencies have yet to come to any firm conclusions.
Theories abound, including that the injuries are byproducts of surveillance technology or that they are deliberate attempts to inflict harm, but all remain unproven so far.
Nevertheless, Mr. Burns was angered by the incident in India, current and former officials said. Some former officials suggested that if it was an attack and an adversarial power was responsible, striking at Mr. Burns’ delegation would amount to an egregious escalation.
The incident in India was reported earlier by CNN.
Mr. Burns has made investigating the anomalous health incidents attributed to Havana syndrome a top priority, creating a targeting cell to investigate the incidents and improving medical care for those who have been injured by them.
Nearly half of the known cases involve C.I.A. officers, although State Department diplomats and members of the military have also been affected, officials have said.
Last month, Vice President Kamala Harris was delayed for three hours as she was about to fly to Hanoi, after an American official in Vietnam reported Havana syndrome symptoms.
Current and former officials said there is no sign of the incidents trailing off, and some people believe they could be increasing.
Government agencies have been stepping up warnings about the incidents in recent days, particularly for officials traveling abroad. Last week the Pentagon warned its entire work force about the anomalous health incidents, which it said often involve strange sounds or a sensation of heat or pressure followed by headache, nausea, vertigo and other symptoms.
The new government warnings have all told officials that if they experience such sensations or symptoms to immediately leave the area they are in.
A C.I.A. spokeswoman said the agency does not comment on specific incidents or officers. But she said the agency’s protocols for health incidents include ensuring officers receive prompt medical treatment.
The spokeswoman outlined the steps the agency and Mr. Burns have taken to improve the response and treatment of Havana syndrome incidents, including making changes to the Office of Medical Services and working with a panel of experts from across the intelligence agencies and private sector to better understand the episodes.
While some officials believe the incidents could go back years, including to the Cold War, the most recent spate began at the American Embassy in Havana, where diplomats and C.I.A. officers reported hearing strange sounds and then feeling headaches and nausea.
That was followed by a series of incidents at U.S. diplomatic outposts in China that left a number of American officials badly injured. Since then, cases have been reported throughout Asia and Europe.