By Ana Swanson and Edward Wong

WASHINGTON — The most probable cause of a series of mysterious afflictions that have sickened American spies and diplomats abroad in the past several years was radio-frequency energy, a type of radiation that includes microwaves, the National Academies of Sciences, Engineering, and Medicine has concluded in a report.

The conclusion by a committee of 19 experts in medicine and other fields cited “directed, pulsed radio-frequency energy” as “the most plausible mechanism” to explain the illness, which came to be known as Havana syndrome, although they said that they could not rule out other possible causes and that secondary factors may have contributed to symptoms, according to a copy of the report obtained by The New York Times.

The report, which was commissioned by the State Department, provides the most definitive explanation yet of the strange illness that struck scores of government employees, first at the US Embassy in Havana in 2016 and subsequently in China and other countries. Many of the officers suffered from dizziness, fatigue, headaches and loss of hearing, memory and balance, and some were forced into permanent retirement.

CIA officers visiting overseas stations experienced similar symptoms, the Times and GQ magazine reported in October. The officers were travelling to discuss countering Russia covert operations with foreign intelligence agencies, a fact that adds to suspicions that Moscow is behind the episodes.

Although couched in careful, scientific language, the new report reveals strong evidence that the incidents were the result of a malicious attack. It attributes the illnesses to “directed” and “pulsed” — rather than “continuous” — energy, implying that the victims’ exposure was targeted and not the result of more common sources of microwave energy such as, for example, a cellphone.

It also said the committee found the immediate symptoms that patients reported — including strange sensations of pain, pressure and sound that often appeared to emanate from a particular direction or occur in a specific spot in a room — were more consistent with a directed “attack” of radio-frequency energy.

The committee considered other causes, like chemical exposures and infectious diseases, but said they appeared unlikely.

The report said that the variability of the incidents, which appeared to affect people in different ways, left open the possible influence of “psychological and social factors.” And it said that some of the victims may be experiencing a condition called “persistent postural-perceptual dizziness,” a nervous system disorder that produces a prolonged feeling of vertigo or unsteadiness.

The episodes have been the subject of much speculation and controversy. Many of the victims, as well as some government officials and outside scientists, have long argued that radio-frequency energy was the most likely cause, potentially the result of a weapon wielded by a foreign power.

Several of the victims have accused Secretary of State Mike Pompeo and other Trump administration officials of downplaying the issue in an attempt to avoid disrupting international ties. They now ask how President-elect Joe Biden and his nominee for secretary of state, Antony Blinken, will respond, especially given the new scientific findings.

After lawmakers pressured the State Department for months to release the report, the agency gave it to some congressional officials and others Thursday (3) and Friday (4), asking them not to share it. The Times and NBC News separately obtained the report Friday, and NBC earlier reported the findings. The National Academies publicly released the report Saturday (5) evening.

”We are pleased this report is now out and can add to the data and analyses that may help us come to an eventual conclusion as to what transpired,” the State Department said in a statement Saturday.

The department also said that “each possible cause remains speculative” and that various factors, including the committee’s lack of access to some information because of potential security concerns, “limit the scope of the report,” though “they do not lessen its value.”

For the Trump administration, acknowledging that the incidents were the result of a foreign attack could have necessitated evacuating US missions in China, disrupting an important economic relationship. The administration did take a harder approach in Cuba, which aligned with its larger goal of reversing President Barack Obama’s diplomatic opening with Havana.

The question of Moscow’s possible culpability is a thorny one, given the sensitivities around President Donald Trump on any matters involving Russia or President Vladimir Putin. Moscow has denied any role, and Gina Haspel, CIA director, has not concluded the Kremlin was responsible. But some CIA analysts who are Russia experts, diplomats and scientists contend that evidence points to Moscow, which has a long history of experimenting with the technology.

The report does not point to a perpetrator, although it mentions “significant research in Russia/USSR” on pulsed radio-frequency technology as well as the exposure of military personnel in Eurasian communist countries to microwave radiation. The Soviet Union bombarded the U.S. Embassy in Moscow with microwaves in the 1970s and ’80s. In a 2014 document, the National Security Agency discussed a microwave weapon used by a hostile country, which people familiar with the document said was Russia.

Mark Lenzi, a diplomatic security officer who was afflicted with the symptoms while working in Guangzhou, China, in early 2018, said that the administration’s treatment of its employees, including its efforts to “deny and cover up inconvenient scientific and medical facts,” had left him angrier at his own government than the government that injured him.

“My government looked the other way when they knew I and my family were injured,” he said. “This report is just the beginning, and when the American people know the full extent of this administration’s cover-up of the radio-frequency attacks in China in particular, they will be outraged.”

Lenzi has sued the State Department for disability discrimination. The Office of Special Counsel has been pursuing two investigations into the State Department’s conduct.

Some family members of the affected US government employees also fell ill overseas, including Lenzi’s wife. And at least 14 Canadian citizens in Havana said they had experienced similar symptoms.

The report by the National Academies also contains a stark warning about the possibility of future episodes, and the US government’s ability to detect them, or to mount a response. The fact that American government employees reported afflictions not only in Cuba and China but also in Russia and other countries raises questions about how widespread the incidents may be.

The committee was not in a position to assess “specific scenarios involving malevolent actors,” David Relman, a Stanford University professor who led the committee, wrote in a preface to the report. Yet, he said, “the mere consideration of such a scenario raises grave concerns about a world with disinhibited malevolent actors and new tools for causing harm to others.”

The report recommends that the State Department act now to establish plans and protocols so it can immediately begin an investigation if similar incidents occur.

“The larger issue is preparedness for new and unknown threats that might compromise the health and safety of US diplomats serving abroad,” the report concludes. “The next event may be even more dispersed in time and place, and even more difficult to recognize quickly.”

Several lawmakers have forcefully pressed the State Department to be more accountable and provide proper health and work compensation benefits to all of the victims and affected family members. Sen. Jeanne Shaheen, D-NH, has inserted a provision on long-term benefits into the latest defence budget bill that Congress is expected to pass this month, although Trump has threatened to veto the measure for reasons unrelated to the provision.

-New York Times