The United States is kicking out 15 of Cuba's diplomats in a row over alleged attacks on US staff in Havana.
US secretary of state Rex Tillerson said the move would "ensure equity".
He said the decision was made "due to Cuba's failure to take appropriate steps to protect our diplomats".
He was referring to unexplained attacks in Havana that have allegedly harmed at least 22 American government workers and their family members.
Mr Tillerson said the US is maintaining diplomatic relations and will cooperate with Cuba while the investigation continues.
But he said his decision to withdraw 60% of US diplomats from the embassy in Havana will remain in effect until Cuba can ensure that American diplomats there are safe.
He said the move was needed to "minimise the number of diplomats at risk of exposure to harm".
Washington has given Cuba a list of 15 of its diplomats who must leave the US within seven days although they are not being declared "persona non grata".
That designation would prevent them ever from returning.