HAVANA — Secretary of State Rex Tillerson said Friday that U.S. diplomats in Havana had been the victims of “health attacks” that left them with hearing loss, the most definitive U.S. statement yet on a series of incidents that have puzzled longtime observers of U.S.-Cuban relations.

His comments came two days after the State Department issued a vaguely worded statement saying there had been “incidents which have caused a variety of physical symptoms.”

U.S. officials later revealed that American diplomats had suffered unexplained losses of hearing, and on Thursday Canada’s government said at least one Canadian diplomat in Cuba also had been treated for hearing loss.

“We hold the Cuban authorities responsible for finding out who is carrying out these health attacks on not just our diplomats, but as you’ve seen now, there are other cases with other diplomats involved,” Tillerson said in Bedminster, N.J., where President Donald Trump and members of his administration spoke to reporters.

In the fall of 2016, a series of U.S. diplomats began suffering unexplained losses of hearing, according to officials with knowledge of the case. Some of the diplomats’ symptoms were so severe that they were forced to cancel their tours early and return to the United States, the officials said.

The officials told The Associated Press that the hearing loss appeared to have been caused by the deliberate use of some sort of sonic device operating outside the range of audible sound.

Former U.S. and Canadian diplomats said they had been targets of low-level harassment and intimidation by Cuban agents in the 1980s, 1990s and 2000s, incidents that included attacks on diplomats’ pets and intimidating maneuvers like tailgating and flashing bright lights into diplomats’ cars as they drove with their families late at night.

“There were things like turning off your electricity, turning off your water, entering your home, leaving little reminders that they were there. Things would be out of place,” said John Caulfield, the head of the U.S. Interests Section in Cuba from 2011 to 2014.

Caulfield said U.S. diplomats in Cuba are under 24-hour surveillance during their assignments.

“Nobody does anything in Cuba without them knowing,” Caulfield said.