The State Department ordered all non-emergency personnel at the U.S. embassy in Havana and their family members to depart Cuba after mysterious ongoing attacks that have severely injured at least 21 people, senior officials said Friday.

The State Department also announced a new travel warning for U.S. citizens to Cuba. Some of the attacks have occurred in hotels, The Associated Press reported.

The evacuation of diplomatic personnel leaves only emergency staff at the American embassy in Havana and suspends embassy operations until the Cuban government can assure the safety of U.S. citizens, officials said. Short-term travel to the island will be limited to officials working on the investigation, and there will be no official diplomatic meetings in Cuba until further notice.

Some embassy personnel have been diagnosed with mild traumatic brain injury and damage to the central nervous system. Others report hearing loss, dizziness, tinnitus, visual complaints, headache, fatigue, cognitive issues and difficulty sleeping.

Ongoing investigations have failed to identify who or what is behind what Secretary of State Rex Tillerson has called “health attacks,” according to senior government officials. Some officials have speculated some kind of sonic attack was directed at the homes of embassy personnel beginning late last year, according to reports.

Tillerson met Tuesday in Washington with Cuban Foreign Minister Bruno Rodriguez to express “profound concern for the safety and security” of diplomatic personnel in Havana, a spokeswoman said. Cuba has been leading its own investigation into the embassy ailments, but has no leads, Rodriguez said.

“The decision to reduce our diplomatic presence in Havana was made to ensure the safety of our personnel,” Tillerson said in a statement. “We maintain diplomatic relations with Cuba, and our work in Cuba continues to be guided by the national security and foreign policy interests of the United States.”

Tillerson and President Donald Trump have spoken against the U.S. rapprochement with Cuba, threatening to undermine the new relationship initiated by former President Barack Obama in 2014 with new travel restrictions and aid cutbacks.