WASHINGTON (CBSNewYork/CBS News/AP) — A series of “specific attacks” on U.S. diplomats has prompted the State Department to issue a travel warning about Cuba and to draw down the amount of diplomatic staff there.

“Over the past several months, numerous U.S. Embassy Havana employees have been targeted in specific attacks,” the warning said. “These employees have suffered significant injuries as a consequence of these attacks. Affected individuals have exhibited a range of physical symptoms including ear complaints and hearing loss, dizziness, headache, fatigue, cognitive issues and difficulty sleeping.”

“Attacks have occurred in U.S. diplomatic residences and hotels frequented by U.S. citizens,” the State Department said in the warning.

The State Department is also pulling “nonemergency U.S. government employees and their family members.” Senior U.S. officials said that amounts to roughly 60 percent of the U.S. diplomatic staff there.

“Due to the drawdown in staff, the U.S. Embassy in Havana has limited ability to assist U.S. citizens,” the State Department said.

The officials say the U.S. is halting visa processing in Cuba indefinitely. They say the steps will remain until Cuba can assure the U.S. its diplomats are safe.

For more information, Americans there are urged to:

CBS News reported Thursday that an internal memo was sent to Secretary of State Rex Tillerson suggesting a drawing down of personnel in Havana. The meeting this week between Tillerson and Cuban Foreign Minister Bruno Eduardo Rodriguez Parrilla did nothing to help assure the U.S. that Cuban officials are doing enough to protect the safety and welfare of U.S. diplomats in their country. Though Cuba is allowing U.S. investigators into the country, it has not convinced the U.S. that it’s taken any real action to prevent the health attacks.

In total, the State Department says there are 21 medically confirmed cases. The attacks were directed at their homes, which the Cuban government provides.  The last reported incident was in August.

(© Copyright 2017 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)