Cuba's independent Commission on Human Rights has denounced the deaths of 26 patients at a psychiatric hospital in one week as a case of "criminal negligence".
The deaths occurred at the Psychiatric Hospital in the capital, Havana, which houses some 2500 patients.
The health ministry originally said natural causes such as old age, respiratory problems and complications from chronic diseases contributed to the deaths, but the commission said that at least 24 of the patients died of hypothermia.
It said the hospital was in such a bad state that it could not protect people from the cold, citing problems including broken windows.
"It is the highest number of avoidable deaths in a Cuban hospital in the history of the republic," it said, adding that the Cuban health system was showing "growing signs of deterioration".
The government has since that a health ministry investigation had already identified "various deficiencies" and that those principally responsible would be sent to trial.
Cuba prides itself on its provision of free universal healthcare.