The United States on Wednesday urged its citizens in China to remain alert after an American citizen working at its consulate in the city of Guangzhou suffered a mild brain injury after months of experiencing abnormal sensations of sound and pressure, Reuters reported.

Secretary of State Mike Pompeo said the United States was concerned about the “serious medical incident” and had raised it with China’s foreign minister Wang Yi, who is in the US at the moment. Pompeo said the medical indications were “very similar” and “entirely consistent” with those experienced by American diplomats posted in the Cuban capital of Havana, CNN reported.

In September, the US had ordered more than half of its diplomats to leave Cuba, a year after they began to describe unexplained health problems. At least 21 of them and their families reported traumatic brain injuries and permanent hearing loss. The symptoms of illness have varied from person to person. In addition to hearing loss and concussions, some experienced nausea, headaches and ear-ringing, and some now suffer from problems with concentration and word recall. Cuba denied being behind the unexplained attacks.

“We notified China of what took place as best we know it and they have responded in a way that is exactly the right response,” Pompeo said at a news conference with Wang. “We are working together to resolve [this]...I hope we can figure it out.”

The Chinese foreign minister said authorities in Beijing were investigating the incident and that they did not have a suspect at the moment.