After Castro tried to poison U.S. diplomats in Havana, two Cuban diplomats have been kicked out of the US.

Two Cuban diplomats were expelled from the U.S. in May after U.S. diplomats stationed in Havana began showing symptoms after a number of undisclosed incidents, State Department spokeswoman Heather Nauert confirmed Wednesday.

Nauert refused to elaborate on the symptoms experienced by the American diplomats, but clarified that they were not life-threatening, after CBSRadio first reported the story. She also revealed that American diplomats have been experiencing “symptoms” since late 2016 and that it was not affecting other U.S. citizens in Cuba. The incidents remain under investigation, and have caused some U.S. diplomats to leave their postings.

“The safety and security of U.S. citizens is our top priority,” Nauert said, adding that “the Cuban government has a responsibility and obligation to protect our diplomats under the Geneva Convention.”

President Donald Trump announced his intent to restrict U.S. citizens ability to travel to Cuba in late June after the Obama administration restored relations with the country in 2016.