WASHINGTON, United States (AFP) — Recent mystery illnesses that have injured 26 US diplomatic personnel and their families in Cuba have prompted a surprise visit by three senior State Department officials to the communist island nation.

The apparent victims of what Washington has called sonic “attacks” have suffered symptoms consistent with mild brain trauma — including, in some cases, disorientation and hearing loss.

Acting Assistant Secretary for Western Hemisphere Affairs Francisco Palmieri, Acting Deputy Under Secretary for Management William Todd and Assistant Secretary for Diplomatic Security Michael Evanoff travelled to Havana to “visit embassy personnel in light of new health attacks against US diplomats at Embassy Havana,” a State Department spokesperson said.

Although the length of the trip was not revealed, CBS News reported that they left Cuba on Tuesday.

“The trip provided an opportunity for our senior officials to gain deeper insight into the unique challenges posed by these attacks and their impact on US operations on the ground,” the US official said.

In June, the State Department indicated that two US diplomats experienced the previous month similar health ailments at an American diplomatic residence where they were both present.

The two cases were the first in Havana since August 2017, bringing the total to 26. The ailments first began in late 2016.

Some American officials in both China and Cuba reported hearing an unidentified noise before falling ill, and initial reports suggested they may have been hit by a secret sonic weapon.

But US intelligence and medical experts have been investigating for more than a year and seem no closer to identifying the cause.

After holding Cuba responsible for either carrying out the attacks or failing to protect its officials, the US recalled more than half of its staff from the embassy and expelled 15 Cuban diplomats from Washington.

This marked a major diplomatic crisis following the countries’ cautious revival of ties in 2015, but Cuba has firmly denied any role in or knowledge of the incident.

On June 10, the Cuban foreign ministry said: “We can confirm that we have no credible hypothesis or scientific explanation that justifies the retaliatory US measures.”