Secretary of State Rex Tillerson said in a statement on October 3: “The decision was made due to Cuba’s failure to take appropriate steps to protect our diplomats in accordance with its obligations under the Vienna Convention. This order will ensure equity in our respective diplomatic operations.”
At least 21 people working at the US’s embassy in Havana have reported health problems, ranging from mild brain trauma and deafness to dizziness and nausea.
Earlier reports suggested sonic attacks were to blame, but nothing has been proven.
Havana denies targeting embassy staff, and the US has not blamed the Cuban government for the suspected attacks.
Rex Tillerson added in his latest statement: “We continue to maintain diplomatic relations with Cuba, and will continue to co-operate with Cuba as we pursue the investigation into these attacks.”
US officials said the expulsions were in protest at Cuba’s failure to protect its diplomats.
Sonic devices may have been used to emit inaudible sound waves that can cause deafness.
On September 1, the US government confirmed that an incident took place as recently as August and that the number of staff reporting problems had increased.
State Department spokeswoman Heather Nauert said: “We can’t rule out new cases as medical professionals continue to evaluate members of the embassy community.”
In a statement, the American Foreign Service Association, which represents US diplomatic and international aid staff, said it had spoken to 10 people who had received treatment.
“Diagnoses include mild traumatic brain injury and permanent hearing loss, with such additional symptoms as loss of balance, severe headaches, cognitive disruption and brain swelling,” the statement said.
The American Foreign Service Association urged the government to do everything possible to help those affected and to “ensure that these incidents cease and are not repeated”.
The statement is the first time that the hearing loss has been described as permanent. It is understood that “mild traumatic brain injury” could include concussion or headaches.
The State Department is yet to blame anyone for the incidents.
The US mission in Cuba was reopened as a full embassy in 2015 following 50 years of hostilities between the two countries.
The United States and Cuba are to announce the opening of embassies in each other’s capitals, a senior US official has said.
The embassies opening is a major step in re-establishing diplomatic ties between the US and Cuba which were severed in 1961.
Relations had been frozen since the early 1960s when the US broke links and imposed a trade embargo with Cuba.
The US and Cuba agreed to normalize relations at the end of 2014.
Presidents Barack Obama and Raul Castro held historic talks in April 2015.
Since 1977, the US and Cuba have operated diplomatic missions called “interests sections” in each other’s capitals under the legal protection of Switzerland. However, they do not enjoy the same status as full embassies.
US officials said President Barack Obama would make a formal announcement from the White House on July 1.
It is still not clear exactly what the date will be for opening the embassies, but it is likely to be in mid-July.
The US State Department must give Congress two weeks’ warning before the embassy can open.
It is the latest major milestone in a thawing process between the two countries’ relations, which started with secret negotiations and was announced last December.
In April, Barack Obama and Raul Castro met for the first formal talks between the two countries’ leaders in more than half a century.
A month later, the US removed Cuba from its list of state sponsors of terrorism. Plans to resume ferry and air services between the US and Cuba were also announced.
Despite the new transport links, a Cuba travel ban is still in place for US citizens.
Cuba is also still subject to a US arms embargo which has been in place since 1962, though President Barack Obama has urged Congress to lift it.
The US broke off diplomatic relations with Cuba in 1959 after Fidel Castro and his brother Raul led a revolution toppling US-backed President Fulgencio Batista. The Castro brothers established a revolutionary socialist state with close ties to the Soviet Union.
In December 2014, Barack Obama and Raul Castro made a surprise announcement saying they would seek to re-establish diplomatic ties, ending more than 50 years of ill-will.