Some of the 1,000 US diplomats and intelligence officers hit by a mysterious illness known as Havana Syndrome could have been targeted by electromagnetic energy pulses, according to a report to US intelligence leaders released on Wednesday.

"Pulse electromagnetic energy, particularly in the radio frequency range, plausibly explains" the ear pain, vertigo, and other symptoms of some of those suffering the ailments first reported by US diplomats in the Cuban capital in 2016, experts from inside and outside the US government said.

The panel of experts was convened by Director of National Intelligence Avril Haines and CIA Deputy Director David Cohen.

The combination of symptoms "cannot be easily explained by known environment or medical conditions" among a subset of victims. The number of those people was not disclosed in the report's unclassified executive summary.

Cases have been reported in Russia, China, Tajikistan and some African countries.

The findings echo a 2020 National Academy of Sciences study and follow a Jan. 20 interim CIA report that concluded that it was unlikely that Russia or another foreign adversary was behind most of the so-called "anomalous health incidents."

The CIA report, however, said there were about two dozen cases of the 1,000 that remained unexplained.

The report released on Wednesday did not delve into responsibility. But its conclusions will likely fuel frustration among current and former U.S. officials who lack a clear explanation for their chronic afflictions.

"We were not looking at attribution or assigning it to a foreign adversary or actor. We stuck to the causal mechanism," a US intelligence official familiar with the report told reporters.

The findings "reinforce the need for a coordinated, whole of government approach," Mark Zaid, a lawyer representing victims from numerous US government agencies, said in a statement. "These piece-meal agency reviews at times reveal inconsistent and even contradictory results."

Eric Lander, director of the White House Office of Science and Technology Policy, said in a statement that the panel worked for nearly nine months and was the first of several expert groups to have such extensive access "to intelligence reporting and patient data."

The panel found that the symptoms "are genuine and compelling" based on medical reports and interviews with physicians and victims.

In finding that "pulsed electromagnetic energy" could be the cause, the panel said "information gaps exist" but there are several plausible ways the energy could have been generated "each with its own requirements, limitations and unknowns."

Such sources exist that "are concealable and have moderate power requirements," the report said. "Using non-standard antennas and techniques, the signals could be propagated with low loss" through the air and building materials.

Individuals accidentally exposed to electromagnetic energy signals - which include radio waves, microwaves and X-rays - have reported "sensations" similar to the symptoms reported by Havana Syndrome victims, the report noted.

Ultrasound also could account for the symptoms, but only if a victim was in close proximity to the beam because ultrasound "propagates poorly through the air and building materials," it continued.

Psychosocial factors - which include work demands, stress and depression - cannot alone account for the core symptoms of Havana Syndrome, it said.

The report offered recommendations to help understand, prevent and manage the afflictions, including collecting and coordinating incident and medical data within the US government.