More American diplomats working for the state department in Cuba have begun showing the effects of a suspected “sonic harassment attack”, the US has confirmed, as authorities in Washington try to get to the bottom of the bizarre series of events.

Heather Nauert, spokesman for the state department, said that there are now 21 reported cases – up from 19 at the beginning of the month.

Diplomats and their families have reported hearing loss and nausea, with some even being diagnosed with mild traumatic brain injuries.

The Trump administration has not blamed the Cuban government for what the union representing Foreign Service officers called “sonic harassment attacks” dating to late 2016.

Cuba has denied orchestrating an attack on the diplomats, and analysts are puzzled.