At least 21 members of the US mission in Havana and a smaller number of Canadians have suffered brain injuries and hearing loss in what have been reported as "acoustic attacks", although US officials say their origin remains unclear.
The incidents began last year, and the latest was recorded in August, despite US authorities having complained to Cuban officials in February and having expelled two Cuban diplomats from Washington in May.
The mission remains open, and US officials have warned that Cuba is responsible for the safety of diplomats on its soil, without accusing them directly.
With the injury toll continuing to rise, and no explanation for what Washington has called an "unprecedented incident," some US lawmakers have called for the embassy to be closed down once again.
Asked about this on CBS News' Face the Nation, Tillerson did not rule this out.
"We have it under evaluation. It's a very serious issue with respect to the harm that certain individuals have suffered," he said.
US officials have told reporters they believe some kind of sonic device was used to covertly undermine the health of staff members at the mission, who began reporting sick last year.
The American Foreign Service Association -- the labor union representing US diplomats -- spoke to 10 of those who received treatment and said their diagnoses included mild traumatic brain injury and permanent hearing loss.
At least five Canadian diplomats and their families were also affected by "sonic attacks," though none suffered permanent injury, public broadcaster CBC reported Friday. Canada has said Cuban officials are not suspected.
On Thursday, State Department spokeswoman Heather Nauert confirmed the number of Americans hurt had risen to 21.
"We hope that that number will not increase. We certainly can't count that out. We are having our people medically tested," she told reporters.
"Our folks are able to leave Havana, leave Cuba, and return back home if they wish to do so -- I think we call it compassionate curtailment or something like that -- where they're able to switch out a job," she said.
The State Department, citing respect for the privacy of its employees, has not discussed the diplomats' symptoms publicly, but Nauert said the form of injury "can be different in different people."
Relations between the United States and Cuba were restored by then president Barack Obama and his counterpart Raul Castro in 2015 after a half-century.
But tensions mounted again after Obama's successor Donald Trump, who won many Cuban American votes by promising a tough line, rolled back detente.
Disclaimer: No Business Standard Journalist was involved in creation of this content
You’ve reached your limit of {{free_limit}} free articles this month.
Subscribe now for unlimited access.
Already subscribed? Log in
Subscribe to read the full story →
Smart Quarterly
₹900
3 Months
₹300/Month
Smart Essential
₹2,700
1 Year
₹225/Month
Super Saver
₹3,900
2 Years
₹162/Month
Renews automatically, cancel anytime
Here’s what’s included in our digital subscription plans
Exclusive premium stories online
Over 30 premium stories daily, handpicked by our editors


Complimentary Access to The New York Times
News, Games, Cooking, Audio, Wirecutter & The Athletic
Business Standard Epaper
Digital replica of our daily newspaper — with options to read, save, and share


Curated Newsletters
Insights on markets, finance, politics, tech, and more delivered to your inbox
Market Analysis & Investment Insights
In-depth market analysis & insights with access to The Smart Investor


Archives
Repository of articles and publications dating back to 1997
Ad-free Reading
Uninterrupted reading experience with no advertisements


Seamless Access Across All Devices
Access Business Standard across devices — mobile, tablet, or PC, via web or app
