It is not known how long the suspension of the visa reunification program will last.

The withdrawal of more than half of the American staff from the embassy in Havana is in response to mysterious sonic attacks that have caused several health problems to at least 21 diplomats, officials confirmed.

Additionally, Washington has issued a new alert warning Americans not to travel to the island because of the attacks.

"Over the past several months, numerous U.S. Embassy Havana employees have been targeted in specific attacks," the State Department said in its notice. "These employees have suffered significant injuries as a consequence of these attacks. Affected individuals have exhibited a range of physical symptoms including ear complaints and hearing loss, dizziness, headache, fatigue, cognitive issues, and difficulty sleeping."

Beyond the family reunification program, all other visas — immigrant and non-immigrant — also will be "suspended indefinitely."