Washington - US Secretary of State Rex Tillerson said on Sunday that Washington is considering the possibility of closing its embassy in Havana in the wake of a mysterious "sonic attack" that left several of its staff with brain injuries and hearing loss.Washington says at least 16 employees at its Havana embassy - which fully reopened in 2015 after a half-century breakdown in diplomatic relations - were injured in a series of incidents that began last year.The State Department has called the attacks "unprecedented" and has warned Havana it is responsible for the safety of envoys working on its soil - without saying who it believes was behind them.Asked on CBS's "Face the Nation" about a call by several US lawmakers to close down the embassy, Tillerson responded:"We have it under evaluation. It's a very serious issue with respect to the harm that certain individuals have suffered.""We've brought some of those people home," he added. "It's under review."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. Some of the 16 staff who were hurt were evacuated to Miami for treatment in US hospitals, while others were cared for by American doctors who travelled to Havana to work at the embassy.The American Foreign Service Association - the labour union representing US diplomatic and international aid personnel - 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 on Friday. Canadian authorities have said Cuban officials are not suspected.