The US is testing two staff members from its Cuban embassy in Havana amid concerns they may have been subjected to sonic attacks.
A State Department spokesman said they were being tested for brain injuries.
Last year, 24 Cuba embassy staff suffered a mysterious illness after reporting "auditory sensations".
Earlier this week the US removed diplomats from the southern Chinese city of Guangzhou, after they reported symptoms and strange sounds.
The incidents have raised concerns that a government or agency may be targeting the US with a new type of sonic weapon.
Cuba has denied targeting embassy staff, and the US has not blamed the country's government for the suspected attacks.
Those affected have suffered a range of symptoms including hearing loss, dizziness, fatigue, cognitive issues and sleep loss.
The two latest staff members from the Cuba embassy could be "potentially new cases" but are yet to be "medically confirmed," a US State Department official told the Associated Press news agency.
They are said to have been taken to the University of Pennsylvania, where doctors are treating those with suspected injuries.
Last month, the US State Department urged its staff in China to alert them to any abnormal hearing or vision issues after an employee reported mystery symptoms.