Secretary of State Rex Tillerson Rex Wayne TillersonGary Cohn: 'I haven't made up my mind' on vote for president in November Kushner says 'Alice in Wonderland' describes Trump presidency: Woodward book Conspicuous by their absence from the Republican Convention MORE said Sunday that closing down the United States’ Embassy in Cuba is “under review” after diplomats working in the country suffered brain injuries.

“We have it under evaluation. It’s a very serious issue with respect to the harm that certain individuals have suffered,” Tillerson told CBS’s “Face the Nation.”

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“We’ve brought some of those people home. It’s under review,” he said.

The Associated Press reported last week that United States officials are still searching for an explanation for the unexplained attacks, which have affected at least 21 diplomats working in Cuba.

Last week, five GOP senators urged the administration to shutter the embassy, saying Cuba failed to protect diplomats. Cuba has denied any involvement in the mysterious acoustic attacks, which left some Americans with permanent hearing loss and mild brain damage.