American-Cuban relations are under severe strain after more than half the personnel at the American Embassy in Havana, Cuba, were withdrawn in the wake of what the State Department has described as a mysterious and sustained ‘sonic’ attack.

It follows 21 embassy staffers reporting illnesses in recent months, including hearing loss, dizziness, tinnitus, balance problems, visual complains, headache, fatigue, cognitive issues and difficulty sleeping.

The New York Times reported the symptoms were caused by ‘some kind of sonic wave machine’, a weapon that operates outside of the range of audible sound to create physical effects.

The University of Miami has been tasked with determining the cause of the ‘health attacks’ following a “nervous call” from the Trump administration, according to the paper.

The Guardian reported some US diplomats hearing “various loud noises or feeling vibrations”, while others heard and felt nothing but reported symptoms later.

Some diplomats were even able to walk “in and out” of the noises in certain parts of the room.

The US State Department ordered the departure of “non-emergency” personnel at the embassy, including family members, and has issued an advisory to Americans to not travel to Cuba.

“Until the government of Cuba can assure the United States of the safety of US government personnel in Cuba, our embassy will be reduced to emergency personnel so as to minimise the number of US government personnel at risk of exposure,” a senior State Department official told reporters on Friday.

“Routine visa operations are suspended indefinitely,” the official said, who spoke to reporters anonymously via a conference phone call.

The Cuban government has denied any role and is investigating the attack, calling Friday’s decision to withdraw US personnel “hasty” and saying it would “affect the bilateral relations”.

In a statement, Secretary of State Rex Tillerson repeated the US assertion that embassy personnel were deliberately targeted, but stopped short of blaming Cuba.

“Cuba has told us it will continue to investigate the attacks, and we’ll continue to cooperate with them in this effort,” Mr Tillerson said.

The Secretary of State said there were no reports private US citizens had been affected, but attacks were known to have occurred in US diplomatic residencies and hotels frequented by American citizens.

“The Department does not have definitive answers on the cause or the source of the attacks and is unable to recommend a means to mitigate exposure,” he said.

A senior State Department official said neither the US nor Cuban governments had been able to identify who was responsible for the attacks but stressed “the government of Cuba is responsible for taking all appropriate steps to prevent attacks on our diplomatic personnel in Cuba”

“Because our personnel’s safety is at risk and we are unable to identify the source of the attack, we believe that US citizens may also be at risk and warn them not to travel to Cuba,” the official added.

– with AAP