The Trump administration is considering closing down the recently reopened US Embassy in Havana following a string of unexplained incidents harming the health of American diplomats in Cuba.
The comments, by Secretary of State Rex Tillerson, are the strongest indication to date that the US might mount a major diplomatic response, potentially jeopardising the historic restart of relations between the US and Cuba.
The two former foes reopened embassies in Washington and Havana in 2015 after a half-century of estrangement.
"We have it under evaluation," Tillerson said of a possible embassy closure. "It's a very serious issue with respect to the harm that certain individuals have suffered. We've brought some of those people home. It's under review."
Of the 21 medically confirmed US victims - diplomats and their families - some have permanent hearing loss or concussions, while others suffered nausea, headaches and ear-ringing. Some are struggling with concentration or common word recall.
Some victims felt vibrations or heard loud sounds mysteriously audible in only parts of rooms, leading investigators to consider a potential "sonic attack." Others heard nothing but later developed symptoms.
Tillerson once called the events "health attacks," but the State Department has since used the term "incidents" while emphasising the US still doesn't know what has occurred. Cuba has denied any involvement or responsibility but stressed it's eager to help the US resolve the matter.
The US has said the tally of Americans affected could grow as more cases are potentially detected.
