The United States is considering closing its embassy in Havana in response to an alleged sonic attack on U.S. personnel in Cuba, Secretary of State Rex Tillerson said on Sunday.

"We have it under evaluation," Tillerson said on CBS' "Face the Nation" program. "It's a very serious issue with respect to the harm that certain individuals have suffered."

Five Republican senators on Friday called for the Trump administration to retaliate against the Cuban government by expelling Cuban diplomats and possibly shuttering the U.S. embassy there over attacks that began in late 2016.

The State Department said in August that Americans linked to the U.S. embassy in Havana had experienced physical symptoms from "incidents" involving sound waves. Five Canadians were also affected.

Symptoms included nausea, dizziness and temporary loss of hearing or memory. Cuba, the United States and Canada have investigated the attacks, but the probe has not yielded any answers about how they were carried out or who was responsible for them.

Cuba has denied involvement. The U.S. State Department has not blamed Havana for the attacks but asked two Cuban diplomats to leave Washington in May.