William Burns announced Friday night that about 100 CIA officers and family members are among the 200 U.S. officials and associates with Havana Syndrome.
"He has stepped up his efforts to determine the cause and responsibility of the syndrome," said Burns, director of the CIA.
Burns noted that a delegation from the US National Academy of Sciences found in December that an acceptable theory was that "directed energy" radiation was causing the syndrome.
The head of the CIA claimed that there was a very strong possibility that the syndrome was intentional and that Russia could be responsible.
Earlier, US State Department spokesman Ned Price confirmed that a number of US diplomats in the Austrian capital Vienna had contracted an unknown disease, and announced that the US government was investigating the mysterious "attacks".
"Since US President Joe Biden came to power, 25 American diplomats or officials in Vienna, Austria, have been involved in these 'attacks' with symptoms similar to Havana Syndrome," The New Yorker reported.