U.S. Secretary of State Rex Tillerson met with Cuban Foreign Minister Bruno Rodriguez on Tuesday to discuss the incidents that caused physical symptoms in Americans serving at the U.S. Embassy in Havana.
U.S. State Department spokesperson Heather Nauert said the two top diplomats had a "firm and frank" discussion of U.S. concern for its employees.
The meeting was the first highest-level diplomatic contact between the two countries since Donald Trump became U.S. president in January.
"The Secretary conveyed the gravity of the situation and underscored the Cuban authorities' obligations to protect Embassy staff and their families under the Vienna Convention," said Nauert.
The U.S. authorities confirmed last month that at least 21 Americans working at the U.S. embassy in Havana suffered physical symptoms.
No details of the injuries have been released, but media reports said the affected Americans suffered a severe hearing loss and at least one victim suffered some "brain damage." ' Earlier this month, Tillerson said that the United States was considering whether or not to close down the U.S. embassy in Cuba following the incidents.
"We have it under evaluation and it's a very serious issue with respect to the harm some individuals have suffered," said Tillerson. "We've brought some of those people home. It's under review."
Rodiguez told Tillerson at the meeting "that according to the preliminary results obtained by the Cuban authorities in their investigations, which have borne in mind the information given by the U.S. authorities, there is no evidence so far of the cause or the origin of the health disorders reported by the U.S. diplomats," Cuba's embassy in Washington said in a statement.
The United States expelled two Cuban diplomats in late May over the incidents. Cuba said that it was investigating the "incidents".
"Cuba has never, nor would it ever, allow the Cuban territory to be used for any action against accredited diplomatic agents or their families," the foreign ministry said in a statement.
The United States and Cuba officially resumed a diplomatic relationship in July 2015, more than five decades after they severed it.