Mysterious incidents affecting the health of American diplomats in Cuba continued as recently as August, the US has said, despite its earlier assessments that the attacks had long stopped.
The US increased its tally of government personnel affected to 19.
The new disclosures came the same day that the union representing American diplomats said mild traumatic brain injury was among the diagnoses given to diplomats hit by the attacks.
In the most detailed account of the symptoms to date, the American Foreign Service Association said permanent hearing loss was another diagnosis, and that additional symptoms had included brain swelling, severe headaches, loss of balance and "cognitive disruption".
US state department spokeswoman Heather Nauert said the US was continually revising its assessments of the scope of the attacks as new information was obtained, and that the investigation had not been completed.
"We can confirm another incident which occurred last month and is now part of the investigation," she said.
US officials had previously said the attacks, initially believed to be caused by a potential covert sonic device, had started in autumn last year and continued until this spring 2017.
Last week, Ms Nauert had 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 assessment indicated investigators were still far off from any thorough understanding of what transpired in the attacks, described by the US as unprecedented.
The fact there was an incident as recently as August suggested the attacks probably 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.
The US has avoided accusing Cuba's government of being behind the attacks. It did expel two Cuban diplomats, but the state department said that was in protest against the Cubans' failure to protect the safety of American diplomats while on their soil, not an indication that it felt that Havana masterminded it.
US investigators have been 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 nothing has been found.
A Canadian government official said it first learned in March 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.
It is 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.
The AFSA said it had met or spoken to 10 diplomats affected, but did not specify how many of them had been diagnosed with hearing loss or with mild traumatic brain injury, commonly called a concussion.
The confirmation that at least some diplomats suffered brain injury suggested the attacks caused more serious damage than the hearing-related complaints that were initially reported.