OTTAWA—The federal government sent a doctor to Cuba to examine Canadian diplomats who suffered everything from nosebleeds to short-term memory loss amid concern about mysterious acoustic attacks, newly declassified memos show.

The June visit to Havana by Dr. Jeffrey Chernin of Health Canada revealed symptoms similar to those experienced by U.S. personnel in Cuba, the internal Global Affairs Canada notes say.

Word of the perplexing phenomenon — which remains unexplained — emerged during the summer, prompting the United States to bring many diplomats home from Havana and to expel Cuban representatives from Washington.

Read more: Doctors discover brain abnormalities in U.S. victims of mysterious invisible attacks in Cuba

In August, Ottawa acknowledged that an unspecified number of Canadians in Cuba had been affected, but Global Affairs has said little about the events.

The newly disclosed records, obtained by The Canadian Press under the Access to Information Act, show that as early as May, Canada’s mission in Havana was seeking help in working out “next steps” for Canadian staff having problems.

“Many of the symptoms are similar to signs of extreme stress, and there is the possibility that there could be mental health effects caused by the fear of being targeted,” wrote diplomat Karen Foss. “Either way, testing should help to rule out cases and reassure personnel that we have the means to be able to provide duty of care.”

Symptoms included headaches, dizziness, nausea, hearing loss, nosebleeds and cognitive issues including loss of short-term memory.

But Canadian officials were puzzled about who or what might have been behind the purported attacks.

“There are no answers,” Foss wrote in a May 28 email. “We are left to (sift through) what we know about ... the targets and possible suspects.”

About a week later, Foss advised that the head of Canada’s mission in Cuba had called a meeting of staff to advise of the “increased threat level.”

A security situation overview noted a need to review who in the mission “is most vulnerable because of any pre-existing condition or other consideration that means they are at greater risk if they are targeted.”

Canadian officials quietly began drafting statements in case the “situation is leaked to the press” — noting there were hints the issue was being discussed at a Virginia school.

By June 9, the mission was underscoring the need for help from a federal medical adviser and stressing that new diplomatic personnel bound for Cuba should be made aware as soon as possible of the strange ailments affecting staff.

Local guards were asked to increase their patrols around the residential properties of Canadian staff and to be extra vigilant in reporting.

Dr. Chernin arrived in Havana on June 18 to meet concerned staff individually and take part in a townhall-style meeting a few days later. The doctor found that symptoms, experience and recovery varied, but he seemed to rule out viral causes such as the flu or hearing loss due to age.

Privy Council Office and Global Affairs Canada officials held a subsequent meeting with Cuban counterparts to encourage “closer collaboration” on fact-finding, explore the possibility of greater security in areas where Canadian diplomats were living “to discourage further attacks” and express Canada’s ongoing commitment to good relations.

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All Canadian personnel experiencing symptoms have undergone testing in Canada or the U.S., Global Affairs spokeswoman Sujata Raisinghani said Thursday.

However, she declined to say how many diplomats and family members have been affected.

“The government of Canada continues to work closely with Cuban authorities to ascertain the cause of these unusual symptoms.”