My guess is that Cuba was testing some new form of surveillance equipment that had unintended consequences.

The US is withdrawing more than half of its staff at its embassy in Cuba in response to mysterious attacks which left its diplomats unwell.

Washington is also warning Americans not to visit the country because some attacks occurred in hotels.

At least 21 staff reported health problems ranging from mild brain trauma and deafness to dizziness and nausea.

Earlier reports suggested that sonic attacks were to blame. Cuba denies any involvement in them.

At least two Canadians were also affected.