At least 19 American diplomats in Cuba have been affected by mysterious attacks blamed on a secret sonic weapon, the United States said on Friday.

US officials said the bizarre incidents took place as recently as August, despite earlier assessments that they had long stopped.

The new disclosures came the same day the union representing American diplomats said mild traumatic brain injury was among the diagnoses given to diplomats victimised in the attacks.

In the most detailed account of the symptoms to date, the American Foreign Service Association (AFSA) said permanent hearing loss was another diagnosis, and that additional symptoms had included brain swelling, severe headaches, loss of balance and “cognitive disruption”.

State Department spokesperson Heather Nauert said the US was continually revising its assessments of the scope of the attacks as new information was obtained. She said the investigation had not been completed.

“We can confirm another incident which occurred last month and is now part of the investigation,” Ms Nauert said.

US officials had previously said the attacks, initially believed to be caused by a potential covert sonic device, had started in autumn 2016 and continued until spring 2017.

Last week, Ms Nauert said at least 16 Americans associated with the US embassy in Havana had been affected, but that the “incidents” were no longer occurring.

The evolving US assessment indicated investigators were still far off from any thorough understanding of what transpired in the attacks, described by the US as “unprecedented”.

As the bizarre saga has unfolded, the US has encouraged its diplomats to report any strange physical sensations. So it’s unclear whether some symptoms being attributed to the attacks might actually be unrelated.

Still, the fact there was an incident as recently as August suggests the attacks likely continued long after the US government became aware of them and ostensibly raised the issue with the Cuban government, creating even more uncertainty about the timeline and who was responsible.

Notably, the US has avoided accusing Cuba’s government of being behind the attacks. The US did expel two Cuban diplomats, but the State Department emphasised that it was in protest of the Cubans’ failure to protect the safety of American diplomats while on their soil, not an indication the US felt that Havana masterminded it.

US investigators are searching to identify a device that could have harmed the health of the diplomats, believed to have been attacked in their homes in Havana, but officials have said no device has been found.

One of the diplomats affected had arrived over the summer of 2017 to work at the US embassy and was later diagnosed with concussion-like symptoms, said a US official, who declined to specify the symptoms that led the diplomat to report the situation.

And in Canada, a government official said that the Canadian government had first learned in March 2017 that one of its citizens was affected. Ottawa had previously confirmed that at least one Canadian diplomat was involved, but had not revealed any timeline for when it occurred or came to light.

Both the US and Canadian officials demanded anonymity because they weren’t authorised to comment publicly.

Donald Trump's international Presidential trips Show all 22 1 /22 Donald Trump's international Presidential trips Donald Trump's international Presidential trips French President Emmanuel Macron and US President Donald Trump AFP/Getty Images Donald Trump's international Presidential trips French President Emmanuel Macron and US President Donald Trump talk as they leave the Army Museum at Les Invalides in Paris AFP/Getty Images Donald Trump's international Presidential trips German Chancellor Angela Merkel and US President Donald Trump arrive for the group photo at the G7 Taormina summit on the island of Sicily in May 2017 Getty Images Donald Trump's international Presidential trips Mr Trump was pressed on the subject at the G7 summit in Italy Getty Donald Trump's international Presidential trips US President Donald Trump gives a speeech at the Warsaw Uprising Monument on Krasinski Square Getty Donald Trump's international Presidential trips US President Donald Trump and Britain's Prime Minister Theresa May during a ceremony at the NATO headquarters before the start of a summit in Brussels, Belgium Reuters Donald Trump's international Presidential trips Montenegro's Prime Minister Dusko Markovic is seen to the right of Donald Trump at a Nato summit in Brussels REUTERS Donald Trump's international Presidential trips Pope Francis meeting with US President Donald J. Trump EPA Donald Trump's international Presidential trips Pope Francis poses with US President Donald Trump and First Lady Melania Trump AFP/Getty Images Donald Trump's international Presidential trips US President Donald Trump arrives at Palazzo del Quirinale ahead of the meeting with Italian President Sergio Mattarella Ufficio Stampa Presidenza della via Getty Donald Trump's international Presidential trips US President Donald Trump is seen during a joint press conference with the Palestinian leader at the presidential palace in the West Bank city of Bethlehem AFP/Getty Images Donald Trump's international Presidential trips Palestinian president Mahmoud Abbas meets US President Donald Trump PPO via Getty Donald Trump's international Presidential trips Israeli Prime Minister Benjamin Netanyahu speaks with US President Donald Trump prior to the President's departure GPO via Getty Images Donald Trump's international Presidential trips US President Donald Trump and Israel's Prime Minister Benjamin Netanyahu shake hands after delivering a speech at the Israel Museum AFP/Getty Images Donald Trump's international Presidential trips US President Donald Trump and First Lady Melania Trump lay a wreath in the Hall of Remembrance as White House senior advisor Jared Kushner and Ivanka Trump watch on during a visit to the Yad Vashem Holocaust Memorial museum AFP/Getty Images Donald Trump's international Presidential trips US President Donald Trump visit to Yad Vashem Holocaust museum in Jerusalem accompanied by Prime Minister Benjamin Netanyahu GPO via Getty Images Donald Trump's international Presidential trips US President Donald Trump takes his seat before his speech to the Arab Islamic American Summit in Riyadh in Saudi Arabia Reuters Donald Trump's international Presidential trips Saudi Arabia's King Salman bin Abdulaziz al-Saud, US President Donald Trump and US First Lady Melania Trump look at a display of Saudi modern art at the Saudi Royal Court in Riyadh AFP/Getty Images Donald Trump's international Presidential trips US President Donald Trump and Saudi Arabia's King Salman bin Abdulaziz al-Saud take part in a signing ceremony at the Saudi Royal Court in Riyadh AFP/Getty Images Donald Trump's international Presidential trips King Salman presents Donald Trump with The Collar of Abdulaziz al-Saud Medal at the Royal Court Palace on 20 May AP Donald Trump's international Presidential trips US President Donald Trump is welcomed by Saudi King Salman bin Abdulaziz al-Saud upon arrival at King Khalid International Airport in Riyadh AFP/Getty Images Donald Trump's international Presidential trips U.S. President Donald Trump and first lady Melania Trump walk on the South Lawn prior to their first foreign trip Getty Images

It’s unclear whether Canadians were intentionally targeted or whether there could have been collateral damage from an attack aimed at Americans, given that diplomats from various countries often live in the same areas of a foreign capital. US officials have said the Americans were targeted in their homes in Havana, not in the embassy.

Canadian officials have been actively working with US and Cuban authorities to ascertain the cause. A Cuban attack deliberately targeting Canadians would be even more confounding, given that Canada – unlike the US – has long had friendly ties to Cuba.

AFSA, in describing the damage to diplomats’ health, said it had met with or spoken to 10 diplomats affected, but did not specify how many of the 10 had been diagnosed with hearing loss or with mild traumatic brain injury, commonly called a concussion.

Yet the confirmation that at least some diplomats suffered brain injury suggests the attacks caused more serious damage than the hearing-related complaints that were initially reported.

“We can’t rule out new cases as medical professionals continue to evaluate members of the embassy community,” Ms Nauert said. She added that the embassy has a medical officer and has been consistently providing care to those who have reported incidents.

Asked for further details about what the US had learned about the cause or culprit in the attacks, the State Department said it had no more information to share.

Traumatic brain injury, or TBI, typically results from a bump, jolt or other external force that disrupts normal brain functioning, according to the US Centres for Disease Control and Prevention.

Short- and long-term effects can include changes to memory and reasoning, sight and balance, language abilities and emotions.

Not all traumatic brain injuries are the same. Doctors evaluate patients using various clinical metrics such as the Glasgow Coma Scale, in which a numerical score is used to classify TBIs as mild, moderate or severe.

“AFSA strongly encourages the Department of State and the US government to do everything possible to provide appropriate care for those affected, and to work to ensure that these incidents cease and are not repeated,” the union said in a statement.