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MIAMI (CBSMiami) — Some U.S. embassy workers in Havana, Cuba had to come back to the U.S. after suffering “physical symptoms,” prompting an investigation.

“Some U.S. government employees working on official duty have experienced incidents at least since late last year,” said CBS Radio reporter Steve Dorsey.

The AP is reporting that one possibility being considered is whether potentially harmful sonic devices might have been secretly placed inside U.S. diplomats’ residences in Havana, causing hearing loss.

As a result, two officials with the Embassy of Cuba were asked to leave the U.S. back in May.

“Two were asked to leave and they did,” State Department spokeswoman Heather Nauert said Wednesday.

Florida Sen. Marco Rubio released a statement, which read:

“The Cuban government has been harassing U.S. personnel working in Havana for decades. This has not stopped with President Obama’s appeasement. Personal harm to U.S. officials shows the extent the Castro regime will go and clearly violates international norms.”

The State Department said they reminded the Cuban government of its obligation under the Vienna Convention to protect diplomats.

While the State Department stayed mostly mum on what the symptoms were, they did say an investigation is underway.

Nauert said the symptoms felt by the State Department workers did require medical attention, but were not life-threatening. Some left Cuba for medical reasons.

“We had to bring some Americans home. Some Americans chose to come home,” said Nauert.

The department does not have “definitive answers on the source or cause of the incidents,” said a spokesperson for Western Hemisphere Affairs.

Nauert said they first heard about the incidents in late 2016. The “physical symptoms” have since only affected State Department employees but they would not say how many.

The department said they are taking this situation “very seriously” and are working to find out the cause and impact of the incidents.

“The safety and security of American citizens abroad is our top priority,” said Nauert.

An FBI official told CBS News the bureau has also been looking into the issue.

As for Americans traveling to the island nation, Dorsey said there is nothing to worry about.

“No private U.S. citizens are at risk in Havana and they don’t plan to issue any travel alert either,” said Dorsey.

Rep. Ileana Ros-Lehtinen is also assuring American citizens’ safety in a statement Wednesday.

“The Castro regime has a long and documented history of acting in a manner adverse to U.S. national interests. One of our foremost priorities is to ensure our government personnel are safe when serving overseas. Our nation is committed to protecting all American citizens wherever they may be.”