An American citizen working at the U.S. consulate in the southern Chinese city of Guangzhou has reported suffering from abnormal" sounds and pressure leading to a mild brain injury, the U.S. embassy said on Wednesday. China said it was investigating the incident. U.S. Secretary of State Mike Pompeo said the United States was concerned about the "serious medical incident" and raised it with China's visiting State Councillor Wang Yi. Pompeo told a news conference with Wang, "We're working together to resolve [this] ... I hope we can figure it out." The unnamed American citizen ... had reported a variety of "physical symptoms" dating from late 2017. "The clinical findings of this evaluation matched mild traumatic brain injury (MTBI)," the embassy said. "We cannot at this time connect it with what happened in Havana, but we are investigating all possibilities," a U.S. embassy official [said]. The U.S. government ... issued a health alert to Americans in China. "If you experience any unusual acute auditory or sensory phenomena accompanied by unusual sounds or piercing noises, do not attempt to locate their source. Instead, move to a location where the sounds are not present," the emailed alert said. The U.S. government in October expelled 15 Cuban diplomats ... for what it said was Cuba's failure to protect staff at the U.S. embassy in Havana from mysterious health incidents at one point thought to possibly have been acoustic "attacks". The cause of those incidents remains unresolved.