Unusual health attacks on U.S. diplomats in Cuba continued as recently as August despite previous assessments that the activities had stopped in the spring, the U.S. said on Friday.

"We can confirm another incident which occurred last month and is now part of the investigation," State Department spokeswoman Heather Nauert said.

The U.S. is continually revising its assessments of the extent of the attacks as new information is obtained, Nauert said. An investigation has not been completed.

The announcement that the attacks – in which a potential covert sonic device caused a series of issues, including permanent hearing loss – comes after the union representing American diplomats said that mild traumatic brain injury was among the diagnoses given to diplomats victimized in the attack.

The American Foreign Service Association said additional symptoms had included brain swelling, severe headaches, loss of balance and "cognitive disruption."

U.S. officials had previously said that the attacks had started in fall 2016 and continued until spring 2017. Last week, Nauert had said at least 16 Americans associated with the U.S. Embassy in Havana had been affected, but that the "incidents" were no longer occurring. The tally of U.S. government personnel affected jumped to 19 following Friday’s revelation.

The revised assessments suggested that U.S. officials were still a long way from a full understanding of what transpired in the unexplained attacks. U.S. 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.

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

“We hold the Cuban authorities responsible for finding out who is carrying out these health attacks,” Secretary of State Rex Tillerson said last month.

But Cuba’s Ministry of Foreign Affairs released a statement August 9 denying the allegations.

“Cuba has never, nor would it ever, allow that the Cuban territory be used for any action against accredited diplomatic agents or their families, without exception,” the ministry said in a statement. “Moreover, it reiterates its willingness to cooperate in the clarification of this situation.”

Two Cuban diplomats were kicked out of the Washington embassy by the State Department following news of the incidents.

The Associated Press contributed to this report.