Washington (AFP) -

The White House said Thursday that Cuba had not done enough to prevent a series of mystery attacks on US diplomats, but stopped short of accusing Havana of carrying them out.

"We believe that the Cuban government could stop the attacks on our diplomats," said White House Chief of Staff John Kelly.

The mysterious attacks, which US officials initially suggested could have been carried out with some sort of covert acoustic device, have affected at least 22 US embassy staff in Havana.

The last instance occurred in August.

Those affected have exhibited physical symptoms including ear complaints, hearing loss, dizziness, headache, fatigue, cognitive issues, and difficulty sleeping.

In response, the US has withdrawn more than half the personnel from the US embassy in Cuba and ordered the expulsion of 15 Cuban diplomats in the United States.

US relations with Havana were only fully restored in 2015 -- after a half-century Cold War breakdown -- and have deteriorated since President Donald Trump took office in January.