WASHINGTON, United States (AP) — Two more Americans have been confirmed to be affected by unexplained health attacks against US diplomats in Cuba, the United States said Tuesday, raising the total number of victims to 21.

The additional two individuals appear to be cases that were only recently reported but occurred in the past. The State Department said no new, medically confirmed “incidents” have taken place since the most recent one in late August. Earlier this month, the US disclosed there had been another incident in August after previously saying the attacks had stopped.

It’s possible the number could grow even higher as more cases are discovered. State Department spokeswoman Heather Nauert said the US continues to assess American personnel.

The US citizens were members of the American diplomatic community, the US said. Officials have said previously that the incidents, deemed “health attacks” by Secretary of State Rex Tillerson, affected diplomats posted to the Embassy in Havana along with family members who live with them.

The US didn’t say how serious the newly disclosed incidents were. But the State Department said it was providing “the best possible medical evaluation and care” throughout the ordeal, including aid from a medical officer on staff at the embassy.

The union representing American diplomats has said mild traumatic brain injury is among the diagnoses given to some diplomats victimised in the attacks. The American Foreign Service Association has said permanent hearing loss was another diagnosis, and additional symptoms had included brain swelling, severe headaches, loss of balance and “cognitive disruption.”

The evolving US assessment indicated investigators were still far from any thorough understanding of what transpired in the attacks, which started in the fall of 2016. The US has described them 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 turn out to be unrelated.

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 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 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 officials have said no device had been found.