The findings are part of a report released this week which sought to explain the hundreds of cases of brain injuries and other symptoms reported by American personnel around the world.

Seven US agencies looked at roughly 1,500 cases in 96 countries but found many of these were "probably" due to things such as undiagnosed illness, malfunctioning air-conditioning, or electromagnetic waves coming from harmless devices such as a computer mouse.

The report's authors also uncovered evidence that foreign countries were not involved - in some cases the US found its enemies were confused about the allegations, with some of them thinking that Havana syndrome was an American plot.

They found "no credible evidence" that any adversary had acquired a weapon, such as a directed energy beam, that could cause the symptoms reported by people, or a listening device that might hurt people.

The involvement of extra-terrestrials was also ruled out.

Those affected by the illness have reported headaches, memory lapses, nausea, dizziness and other symptoms often linked to traumatic brain injuries, and some have been so ill they have left government employment.

The first cases were reported in 2016 at the US Embassy in Cuba, and these were followed by similar reports from diplomats, intelligence officers and military personnel in the Washington DC area and around the world.

Trump used Havana syndrome to justify tougher sanctions on Cuba, diplomat says

The blame was first laid at Cuba's door but authorities there denied any involvement.

After the report was published, Johana Tablada, deputy director of the US division of Cuba's Foreign Ministry, told The Associated Press: "We're not surprised".

She said that Donald Trump had used the syndrome as an excuse to strengthen sanctions against Cuba while he was president.

She added: "Very harsh measures were taken against our people in Cuba and in the United States that harmed Cuban families, exchanges between our countries (and) caused a downward spiral (of ties) that was practically irreversible."

Report not transparent enough, lawyer says

Mark Zaid, a lawyer for more than two dozen people who have reported injuries, criticised the report.

He said: "Until the shrouds of secrecy are lifted and the analysis that led to today's assertions are available and subject to proper challenge, the alleged conclusions are substantively worthless," he said.

"But the damage it has caused to the morale of the victims, particularly by deflecting from the government's failure to evaluate all the evidence, is real and must be condemned."

'Nothing is more important than the health and wellbeing of our workforce'

Maher Bitar, the White House National Security Council's senior director for intelligence programs, said: "Nothing is more important than the health and wellbeing of our workforce.

"Since the start of the Biden-Harris Administration, we have focused on ensuring that our colleagues have access to the care and support they need."

Read more:
'Emotional trauma' caused illness at US base, not sonic attack
CIA's Vienna station chief recalled after mysterious 'Havana syndrome' hits US spies
Electromagnetic energy pulses could be behind Havana Syndrome illness

CIA Director William Burns in a statement. "We will continue to remain alert to any risks to the health and wellbeing of agency officers, to ensure access to care, and to provide officers the compassion and respect they deserve."

There is also a separate Pentagon review into Havana syndrome that is ongoing.