The US State Department evacuated at least 11 more Americans from China amid reports of bizarre sounds and sensations that have been associated with mild traumatic brain injury, according to The New York Times. And cases of sound attacks appear to be spreading to additional diplomatic stations throughout the country.

Meanwhile, officials reported two additional “medically confirmed” cases of similar mysterious health incidents in Cuba at the end of last month, according to a series of reports by the Associated Press.

The new cases in Cuba bring the total number of Americans affected there to 26. The older cases date as far back as late 2016, while the new cases one confirmed last week and the other confirmed the week before that —stem from an incident in May. The newer cases occurred at a diplomatic residence in which both affected individuals were present. The two individuals were said to suffer similar neurological symptoms that others from the US diplomatic community stationed in Havana had experienced.

The most common of those symptoms included cognitive impairment, balance issues, visual and hearing problems, sleep trouble, and headaches. In February, a team of doctors at University of Pennsylvania’s Perelman School of Medicine reported that clinical evaluations of 21 of the affected individuals indicated that they had sustained “injury to widespread brain networks without an associated history of head trauma.”

As for the personnel in China, doctors in the US have so far only confirmed that one American evacuated from the country has a mild traumatic brain injury. The rest are undergoing further medical evaluation in the US.

The one China-based employee with a confirmed brain injury was stationed at the US consulate in the city of Guangzhou and was the first to be evacuated. That happened in April . The State Department linked the case to “subtle and vague, but abnormal, sensations of sound and pressure” similar to the “sonic” episodes recounted by those stationed Cuba. Since the April evacuation, many other Americans in Guangzhou said they had experienced similar episodes , and more than 250 Americans in China have received preliminary medical evaluations.

But the latest tally of the evacuated suggest that the mysterious health phenomenon may be spreading beyond Guangzhou. At least eight of the evacuated were from there, but one employee was from the consulate in Shanghai, and two were from the embassy in Beijing, the Times noted.

In a statement to press, the State Department suggested that some of those returning for medical assessments may have issues unrelated to the puzzling sound incidents. But the State Department noted that it's working with China in an "ongoing cooperation" to investigate the health cases.

Officials still appear stumped as to what might be causing the odd sounds and sensations, as well as how they may be linked to apparent mild traumatic brain injuries. Some researchers have questioned the neurological testing by Penn doctors, while others have continued to speculate that malfunctioning surveillance equipment, covert weapons, or collective delusion may be behind the cases.